OPINION OF THE COURT
NYGAARD, Circuit Judge.This ease involves a dispute over the appropriate bargaining unit at a health care center resulting from the merger of five separate hospitals. Presbyterian University Hospital d/b/a University of Pittsburgh Medical Center1 filed this petition for review of a final order of the National Labor Relations Board. The NLRB cross-petitioned for enforcement of its order. The union intervened in support of the NLRB’s order. We conclude that there is substantial evidence in the record to support the NLRB’s finding that four telecommunications workers are skilled maintenance employees. We also conclude that the NLRB did not abuse its discretion to determine the appropriate unit when it found that the telecommunications workers at the Presbyterian complex share a community of interest with the skilled maintenance employees in the existing bargaining unit, separate from the skilled maintenance employees at the Montefiore complex. We will therefore deny UPMC’s petition for review and grant the NLRB’s petition for enforcement of its order.
I.
UPMC is a private, non-profit, acute care medical center consisting of approximately forty buildings. UPMC resulted from a series of mergers that began in 1989 between five independent hospitals: Presbyterian and Montefiore University Hospitals (both acute care hospitals), Eye and Ear Hospital, The Falk Clinic, and Western Psychiatric Institute and Clinic. Bridges and tunnels connect the main buildings of this center. As a result of the merger, UPMC has one board of directors, one president, and centralized scheduling and materials management systems. Before the mergers the five hospitals operated under separate licenses; UPMC now operates under a single operating license issued by the Pennsylvania Department of Health.
Since 1972, the union has represented skilled maintenance employees at the Presbyterian complex.2 In August 1993, the union sought to add four employees to the existing skilled maintenance unit through a self-determination election. These four employees work in the. Information Services Division at UPMC’s Presbyterian complex and have the job title of “Telecommunications Specialists (Voice) I.” Telecommunications workers are responsible for installation, support and maintenance of UPMC’s telephone network and work primarily at the Presbyterian complex where the existing unit employees are located.
UPMC opposed the union’s representation, asserting that the telecommunications workers were not properly included in the skilled maintenance employees’ bargaining unit, as *1303defined by the NLRB’s final rule governing the appropriate units in an acute care hospital, 29 C.F.R. § 108.30(a)(5). UPMC further asserted that, even if the telecommunications workers properly could be included in that unit, a self-determination election must also include UPMC’s unrepresented, skilled maintenance employees at the Montefiore complex.
After a hearing, the Regional Director issued a Direction of Election, determining that the telecommunications workers were skilled maintenance employees and that they shared a community of interest with the employees in the existing unit. In a second hearing, the Director addressed the issue of whether all of UPMC’s remaining unrepresented skilled maintenance employees, located at the Montefiore complex, must be included in the voting group with the telecommunications workers in order to have a proper residual election. The Director concluded that the election did not have to include these Montefiore employees, because they worked at a separate facility and UPMC had not overcome the NLRB’s single facility presumption.
On review, the NLRB determined that the Director properly included the telecommunications workers in the existing skilled maintenance unit. The NLRB also determined that the unrepresented skilled maintenance employees located at the Montefiore complex need not be included with the telecommunications workers from the Presbyterian complex in order to have a proper election. According to the NLRB, although the Director had incorrectly applied the single facility presumption, the existing skilled maintenance unit was still appropriately considered a mul-ti-facility unit.3 See Presbyterian Univ. Hosp., 313 N.L.R.B. 1341, 1341-42,1994 WL 237798 (1994). By order of June 1, 1994, based on the telecommunications employees’ self-determination election, the Director certified the Union as their collective bargaining representative and included those employees in the existing skilled maintenance unit.
The union then requested bargaining with UPMC concerning the telecommunications workers, but UPMC refused to recognize the union in order to obtain review of the NLRB’s decision. As expected, the union filed an unfair labor practice charge. In August 1994, the Regional Director issued a Complaint and Notice of Hearing on the matter and the General Counsel filed a motion for summary judgment. The NLRB granted the motion, finding that UPMC violated § 8(a)(1) & (5) of the National Labor Relations Act, 29 U.S.C. § 158(a)(1) & (5), by refusing to bargain concerning the telecommunications employees.
II.
The NLRB’s interpretation of the Act normally is entitled to deference and should be upheld if it is rational. St. Margaret Memorial Hosp. v. NLRB, 991 F.2d 1146, 1151 (3d Cir.1993). We uphold its factual findings if they are “supported by substantial evidence on the record as a whole.” Id. at 1152. Because this case involves the NLRB’s unit determination, we note that a unit may still be upheld on review even if it is not the “most appropriate” unit. See American Hosp. Ass’n v. NLRB, 499 U.S. 606, 610, 111 S.Ct. 1539, 1542, 113 L.Ed.2d 675 (1991). “Whether a unit is appropriate involves a large measure of informed discretion vested in the Board and is rarely to be disturbed.” St. Margaret, 991 F.2d at 1152 (internal quotations omitted). Therefore, UPMC must fight an uphill battle “to show that the Board abused its discretion in determining the appropriateness of the bargaining unit in question.” Id. (internal quotations omitted). See also NLRB v. New Enterprise Stone and Lime Co., 413 F.2d 117, 118 (3d Cir.1969).
The Act expressly delegates responsibility for unit determination to the NLRB. 29 U.S.C. § 159(b) provides, in pertinent part:
The Board shall decide in each case whether, in order to assure to employees the *1304fullest freedom in exercising the rights guaranteed by this subchapter, the unit appropriate for the purposes of collective bargaining shall be the employer unit, craft unit, plan unit, or subdivision thereof....
As a result, “[t]he Board may develop and apply rules regarding appropriate units to circumscribe and to guide its discretion.” St. Margaret, 991 F.2d at 1152.
Special concerns regarding the undue proliferation of bargaining units in the health care industry prompted the NLRB to adopt a final rule. As to acute care hospitals, this final rule provides the appropriate job classifications:
Except in extraordinary circumstances and in circumstances in which there are existing non-conforming units, the following shall be appropriate units, and the only appropriate units, except that if sought by labor organizations, various combinations of units may also be appropriate:
(1) All registered nurses.
(2) All physicians.
(3) All professionals except for registered nurses and physicians.
(4) All technical employees.
(5) All skilled maintenance employees.
(6) All business office clerical employees.
(7) All guards.
(8) All nonprofessional employees except for technical employees, skilled maintenance employees, business office clerical employees, and guards.
29 C.F.R. § 103.30(a). The NLRB, in exercising its discretion through the rulemaking process, heeded the congressional “admonition” in the legislative history to the 1974 Amendments (which brought acute care hospitals within the ambit of the Act) to give due consideration to preventing undue proliferation of bargaining units in the health care industry. American Hosp. Ass’n v. NLRB, 499 U.S. 606, 616-17, 111 S.Ct. 1539, 1545, 113 L.Ed.2d 675 (1991) (upholding the final rule as based on substantial evidence and supported by reasoned analysis). ■
The legislative history to the 1974 Amendments raised concerns regarding unit scope issues.4 As reflected in the rulemaking record, “[t]he Board justified its selection of the individual bargaining units by detailing the factors that supported generalizations as to the appropriateness of those units.” American Hosp. Ass’n, 499 U.S. at 619, 111 S.Ct. at 1546. For example, the NLRB considered past adjudicatory decisions in which units of RNs, technical employees and skilled maintenance employees consistently recurred. See Collective Bargaining in the Health Care Industry, 53 Fed.Reg. 33900, 33903 (Sept. 1, 1988) (second notice of proposed rulemak-ing). The first notice of proposed rulemak-ing indicated that
[t]he Board has in the last 13 years received many hundreds of petitions for health care units. Generally, the units requested have been in approximately six, predictable groupings: registered nurses, other professional employees, technical employees, busines[s] office clerical employees, and skilled maintenance employ-ees_ It is our observation that these groups of employees generally exhibit the same internal characteristics, and relationship to other groups of employees, in one health care facility as do like groups of employees at other facilities.
52 Fed.Reg. 25143^4. Therefore, in promulgating the final rule, the NLRB exercised its discretion to avoid case by case adjudication concerning unit scope issues. See 52 Fed.Reg. 25145.
III.
UPMC first challenges the NLRB’s decision to classify the four telecommunications workers as skilled maintenance employ*1305ees. The NLRB adopted the Director’s decision that they were properly classified as skilled maintenance employees under the final rule, 29 C.F.R. § 103.30(a)(5). 313 N.L.R.B. at 1341. The Director considered the following relevant factors: function and skill level of the telecommunications workers; education, licensing and training; supervision; wages, hours and working conditions; interaction with other employees; labor market and career path; whether they worked on the physical plant; and whether their tasks involve equipment and systems.5
In exhaustive detail, the Director explained why he considered the telecommunications workers skilled maintenance employees. Identifying the specific tasks that these workers have in common with unit employees, the Director found that: the telecommunications workers perform work functions that relate to maintenance of the physical plant; their job requires one to three years of experience; their work involves installing wiring and repairing telephones; they are required to have a high school diploma and one to three years of experience; their wage rates compare to that of other unit employees; they work daylight hours; and they interact regularly with other unit employees, especially electricians. Based on these findings, which are supported by substantial evidence, the Director determined and the NLRB agreed that the telecommunications workers were skilled maintenance employees who shared a community of interest with the existing unit employees.
UPMC argues that the telecommunications workers do not work on its physical plant, but instead work on its information systems network. This distinction is artificial. The employees install the wiring and jacks, which are “woven into the physical plant just as firmly as the wiring and outlets that form the electrical system are woven into it.... [A] telephone system is an integral part of the physical plant.” NLRB Brief at 30.
UPMC characterizes the telecommunications workers as unskilled, even though they use some of the same tools as other unit employees, their installation work is similar to that performed by the electricians, and their job requires that they diagnose telecommunications equipment malfunctions and determine whether that equipment should be repaired or replaced. The mere fact that these employees are unlicensed and uncerti-fied does not automatically exclude them from the unit; other unit members, such as painters and plasterers, are uncredentialed, yet they are considered skilled. UPMC also contends that the telecommunications workers should be excluded because they have different immediate supervisors than the existing unit employees, but the NLRB weighed this factor and determined it was insufficient.
The telecommunications workers are required to have experience with a major telephone or interconnect company, perform tests on telephone wiring and equipment and work alongside unit employees, especially electricians, because telephone wiring is often routed in close proximity to electrical wiring. We find substantial evidence to support the NLRB’s determination that the telecommunications workers constitute “skilled maintenance employees.”
Because the majority of the telecommunications workers’ assignments are within the Presbyterian complex, the NLRB found it appropriate to include them in the existing skilled maintenance unit of employees at the Presbyterian complex. We hold that the NLRB did not abuse its discretion by determining that the four telecommunications workers appropriately could be added to the existing skilled maintenance unit through a self-determination election.
IV.
UPMC next argues that even if the NLRB correctly allowed the telecommunications workers to vote on joining the existing unit, it could not properly allow them to vote without opening the election up to all of UPMC’s skilled maintenance employees; therefore, the NLRB, by not also including *1306the Montefiore skilled maintenance employees in the election, ignored its own rule and abused its discretion.
In determining whether the NLRB followed its own final rule or abused its discretion in defining the appropriate unit for the self-determination election, we are mindful of the NLRB’s broad powers to determine appropriate bargaining units, Libbey-Owens-Ford Co. v. NLRB, 495 F.2d 1195, 1199 (3d Cir.), cert. denied, 419 U.S. 998, 95 S.Ct. 313, 42 L.Ed.2d 272 (1974), and to formulate election procedures and policies. St. Margaret, 991 F.2d at 1152. The NLRB’s underlying factual determinations on this issue are supported by substantial evidence. Although UPMC makes arguments that might be persuasive were we determining the matter de novo, it falls far short of showing that the NLRB abused its discretion when it determined that the skilled maintenance employees at the Presbyterian complex should be treated as a unit distinct from their counterparts at the Montefiore complex.
A.
The NLRB rejected UPMC’s argument that, under the final rule, the existing unit of skilled maintenance employees at the Presbyterian complex constituted an existing non-conforming unit as defined by 29 C.F.R. § 103.30(f)(5).6 313 N.L.R.B. at 1342. The NLRB, in its discretion, also rejected the Director’s decision to consider the unit a single facility unit to which the single facility presumption applied. Instead, the NLRB determined that the existing unit more accurately constituted a conforming, multi-facility unit.7 Id. at 1341-42. It based this decision on the fact that the health care center includes two previously independent acute care hospitals and consists of several, separate buildings, many of which are blocks away from the others. The NLRB noted that, although some of the bufldings are connected by tunnels and bridges, not all of the buildings in the Presbyterian complex are interconnected with the buildings in the Montefiore complex. Thus, based on the peculiarities of UPMC, it concluded that the existing unit employees did not truly work at a single facility. The NLRB expressly found that the existing unit conformed to the final rule, because, except for the four telecommunications workers the union sought to add, the unit encompassed all skilled maintenance employees within the Presbyterian complex.
In order to determine whether, after the hospital mergers, the existing unit remained an appropriate multi-facility unit or whether the skilled maintenance employees working at the Montefiore complex must be included, the NLRB, citing Dezcon, Inc., 295 N.L.R.B. 109, 1989 WL 224117 (1989), examined the traditional community of interest factors, which include:
geographic proximity, local autonomy, employee interchange and interaction, functional integration, terms and conditions of employment, and bargaining history.
Presbyterian Univ. Hosp., 313 N.L.R.B. at 1342.
Applying these factors, the NLRB found the following: 1) the geographic proximity of the Presbyterian complex to the Montefiore complex has not had a substantial impact on the existing skilled maintenance unit’s operations; 2) there is a lack of contact between the employees at the Presbyterian complex and Montefiore complex; 3) there is no interchange or interaction between the groups of Presbyterian skilled maintenance employees and Montefiore skilled maintenance employees,8 and there have never been any joint *1307projects involving them; 4) the employees maintain their respective facilities; 5) material purchases are performed by the respective facilities; 6) job openings at a complex are posted within that complex first, then employer-wide; 7) the telecommunications workers are located at the Presbyterian complex and are responsible for servicing the buildings within that complex; 8) Montefiore has its own switch system and is serviced by outside telecommunications contractors; and most importantly, 9) the Presbyterian skilled maintenance unit has a 20-year-long history of successful and peaceful bargaining. There is substantial evidence in the record to support the NLRB’s findings.
Based on its findings, the NLRB determined that the Presbyterian complex skilled maintenance unit remained a distinct and appropriate unit, and that adding the telecommunications workers would not change “the fact that Presbyterian’s and Montef-iore’s skilled maintenance operations are distinct.” 818 N.L.R.B. at 1343. Thus, the NLRB ruled that the existing unit remained appropriate and that the four telecommunications workers constituted all the employees who were residual to that unit. On petition for enforcement of its order, the NLRB emphasizes the unit’s successful and peaceful 20 year bargaining history and argues that including the four telecommunications workers does not pose a risk of disruption to the existing bargaining relationship, while including the 49 special maintenance employees at the Montefiore complex would cause a potentially disruptive and significant change in the unit’s composition.
B.
UPMC’s main argument is that the NLRB violated its final rule by permitting a separate unit at the Presbyterian complex. UPMC points to the words “all skilled maintenance employees” in the rule, 29 C.F.R. § 103.30(a)(5), and argues that all skilled maintenance employees of UPMC must be treated as a unit, because, as a result of the mergers, UPMC now operates under a single Pennsylvania license. Therefore, UPMC maintains, the NLRB cannot treat its Presbyterian and Montefiore facilities as distinct and must include the Montefiore skilled maintenance employees in a self-determination election.
In support of its argument, UPMC asserts that the final rule makes no distinction between acute care hospitals that are comprised of more than one facility or occupy more than one building and those consisting of only one facility. The NLRB responds that the rule did not make that distinction because it was not intended to affect the NLRB’s discretion to determine through adjudication how many facilities of a single employer (as opposed to which job classifications) to include in an appropriate unit.
We agree with the NLRB. The rule simply does not circumscribe or guide the NLRB’s discretion to determine the facilities to be included in a unit when health care *1308providers merge (indeed, it neither considered nor requested evidence on this issue); it regulates the different job categories to be organized in appropriate units in the health care industry. Nor does the NLRB’s finding that UPMC consists of multiple facilities even though it operates under a single license for an acute care hospital contradict its final rule. In that rule, the NLRB defined an acute care hospital to distinguish such institutions from other health care facilities; it did not delegate its discretion to make multi-facility determinations to state hospital licensing entities. UPMC interprets the rule in an artificially restrictive manner which ignores both reality and the purpose for which the NLRB promulgated it.
The notices of proposed rulemaking and the final rule do not even begin to delve into the issues of mergers and multiple facilities of a single employer-hospital. See Collective Bargaining Units in the Health Care Industry, 52 Fed.Reg. 25142-25149 (July 2, 1987) (notice of proposed rulemaking); 53 Fed.Reg. 339000-33935 (Sept. 1, 1988) (second notice of proposed rulemaking); 54 Fed. Reg. 16336-16348 (April 21,1989) (final rule). They clearly indicate that analysis regarding the number of facilities to be included in a unit of, for example, skilled maintenance employees, will still be appropriate. See 53 Fed.Reg. at 33903 (“[T]he proposed rule does not purport to address the issue of the appropriateness of a single facility when an employer owns a number of facilities, which the Board will continue to address through adjudication. Manor Healthcare Corp., 285 N.L.R.B. [224, 1987 WL 89813 (1987) ].”); see also 54 Fed.Reg. at 16338 n. 2 (The rule merely determines that job classification/scope of an appropriate unit within an acute care hospital need not be continuously relitigated, but the Board will still have to resolve issues of unit composition, including whether a single facility is appropriate.). The fact that the final rule does not discuss merged hospitals made up of originally separate hospitals, health care providers operating hospitals made up of separate facilities, or state licensing terminology referring to the merger of two or more hospitals as a single hospital for licensing purposes, does not prevent the NLRB from considering the actual makeup of various health care entities in order to determine the appropriate number of an employer’s facilities to which it must apply the eight bargaining unit categories. Instead, it simply indicates that the rule does not address the issue. Thus, UPMC’s argument that the final rule decided unit composition issues is wholly unsupported and, in fact, contradicted by the rulemaking record.9
Arguing that prior NLRB precedent requires us to deny enforcement of its order, UPMC cites St. John’s Hospital, 307 N.L.R.B. 767, 1992 WL 122630 (1992). The NLRB in that case required that, if a union representing a non-conforming unit sought to represent residual employees, all residual employees had to be added to an existing unit by means of a self-determination election. Therefore, according to' UPMC, if the telecommunications workers are allowed to vote to join the existing skilled maintenance unit, then all UPMC’s remaining unrepresented skilled maintenance employees must be involved in the self-determination election. This argument is without merit.
St. John’s Hospital does not control the NLRB’s decision here. First, unlike the situation in St. John’s, the NLRB here found that the existing unit was a conforming unit. UPMC’s approach in characterizing the existing unit and single facility units generally as “non-conforming units,” reads a presumption into the rule that the only appropriate unit is an employer-wide unit. We find nothing either in the rule or its rulemaking histo*1309ry to indicate that the NLRB created this unique presumption for acute-care hospitals,
Moreover, St. John’s Hospital involved job classification, not multiple facility, issues. Because the employer in St. John’s Hospital had already recognized splintered units of five different types of skilled maintenance employees, the Regional Director found that a sixth unit made up of remaining, unrepresented skilled maintenance employees would be appropriate. The NLRB, however, found that the five non-conforming units were more than enough and that a sixth unit of skilled maintenance employees would lead to further undue proliferation. It therefore ruled that, in order to represent residual employees, the union must try to add them to one of the existing five non-conforming units, rather than create another non-conforming unit. St. John’s Hospital is plainly distinguishable. The NLRB here simply chose not to disturb the existing Presbyterian skilled maintenance unit and permitted all employees residual to that conforming unit to join it.
C.
UPMC argues that the NLRB failed to consider adequately the effect of the hospital mergers on the unit determination. The NLRB responds that it considered the effect of the mergers, but found, within its discretion, that the existing unit of skilled maintenance employees at the Presbyterian complex retained a sufficiently distinct community of interest to warrant its preservation as an appropriate multi-facility unit in spite of the mergers. The NLRB’s decision accords well with the Act’s mandate that its unit determinations “assure to employees the fullest freedom in exercising [their] rights.” 29 U.S.C. § 159(b). Cf. NLRB v. Western & Southern, Life Insur. Co., 391 F.2d 119, 123 (3d Cir.) (NLRB’s single facility presumption accords well with Act’s policies), cert. denied, 393 U.S. 978, 89 S.Ct. 445, 21 L.Ed.2d 439 (1968). This is not a ease where the NLRB has determined that one group of skilled maintenance employees within the same building or facility as another group should constitute a separate unit. Substantial evidence exists to support the particular distinction found by the NLRB between the Presbyterian and Mon-tefiore complexes, in light of the realities at UPMC.10 By determining as a result of that distinction that the skilled maintenance employees at the Presbyterian complex constitute an appropriate unit, the NLRB did not abuse its broad discretion.
The NLRB’s rulemaking process and the decision in Staten Island Univ. Hosp. v. NLRB, 24 F.3d 450 (2d Cir.1994), further convince us that multi-facility analysis was not affected by the final rule and remains relevant to the NLRB’s discretion to determine what group of any of the eight types of employees listed in the Rule constitute an appropriate unit in the health care industry.11 In Staten Island, the court addressed the issue of whether the registered nurses at a North site facility could be treated as a separate bargaining unit from the registered nurses at a South site facility of the same hospital. The separate facilities resulted from the merger of two separate hospitals. The court stated that proper unit determination findings depend on “the degree to which employees in separate locations share a community of interests distinct from their interests as employees of the whole institution.” Id. at 454. The court in Staten Island measured the degree of shared interests by the same factors utilized by the NLRB in this case. Analyzing those factors, it found that the NLRB did not abuse its discretion by determining that the groups of registered nurses at the two different sites constituted separate bargaining units.
D.
UPMC treats its skilled maintenance employees at Presbyterian and Montefiore as *1310separate and distinct in serving their respective facilities. UPMC has no plans to integrate or merge the work of the two maintenance departments. The NLRB, accordingly, has merely applied its broad discretion to the particular circumstances of this case in finding the existing unit appropriate and in conformity with the Final Rule. UPMC has not met its heavy burden to show that the NLRB abused its discretion in that determination.
V.
In sum, we find that the NLRB did not abuse its discretion when it determined that the telecommunications workers could vote to include themselves in the existing skilled maintenance unit at the Presbyterian facility. Likewise, the NLRB’s decision that the skilled maintenance employees at the Mon-tefiore facility did not have to be included in the existing unit was not an abuse of discretion. We also find that the NLRB properly concluded that UPMC violated § 8(a)(1) & (5) of the National Labor Relations Act by refusing to bargain with the Union concerning the four telecommunications employees who unanimously voted to be included in the existing skilled maintenance unit. Therefore, we will deny UPMC’s petition for review and grant the NLRB’s petition for enforcement.
. Presbyterian University Hospital, the surviving corporate entity resulting from the mergers, does business as UPMC pursuant to a fictitious name filing with the Pennsylvania Department of State.
. The present unit employees work exclusively at what the NLRB calls the Presbyterian complex, consisting of Presbyterian and Falk (formerly independent hospitals), as well as additional buildings, but not Montefiore. The unrepresented skilled maintenance employees work in what the NLRB calls the Montefiore complex, consisting of Montefiore and Eye and Ear Institute (formerly independent hospitals), as well as other buildings. These buildings are grouped near the central buildings of the Presbyterian complex.
. A multi-facility unit is a unit of employees made up of the various employees at more than one location or facility of an employer and is also known as a multi-site, multi-plant or multi-location unit. The NLRB uses this term here to refer to the fact that the existing unit is comprised of employees who work in the various facilities that make up the Presbyterian complex. This multi-facility unit, however, does.not encompass all the facilities of UPMC.
. In accordance with the NLRB's use of the terms "unit scope” and "unit composition” in the rulemaking record, we use the term “scope” to refer to the job classifications which make up a separate unit (i.e., whether there should be separate units for skilled and unskilled maintenance workers and whether RNs should be in-eluded with other professionals in a unit), and we use the term "composition” to refer to whether the unit will encompass all the facilities of a single employer, a single facility of an employer with multiple facilities, or some other combination of facilities.
. See Collective Bargaining Units in the Health Care Industry, 53 Fed.Reg. 33900, 33920-21, 33924 (Sept. 1, 1988) (second notice of proposed rulemaking); and Jewish Hospital, 305 N.L.R.B. 955 (1991).
. A non-conforming unit is defined as a unit other than those described in paragraphs (a)(1) through (8) of this section or a combination among those eight units.
29 C.F.R. § 103.30(f)(5).
. The NLRB is not required to apply the single facilily presumption. See NLRB v. Carson Cable TV, 795 F.2d 879, 886-887 (single facility presumption does not apply where NLRB finds a multi-location unit appropriate because under the Act the NLRB need only designate an appropriate unit, not the most appropriate unit).
.UPMC asserts that the NLRB should have focused on employee contact between all the employees of UPMC as opposed to focusing on contact between skilled maintenance employees at the different facilities. The NLRB, quite properly we think, found the lack of interchange among the employees at issue, the skilled maintenance employees at the Presbyterian complex *1307and skilled maintenance employees at the Montefiore complex, entitled to greater weight. See, e.g., NLRB v. New Enterprise Stone & Lime Co., 413 F.2d 117 (3d Cir.1969) (upholding NLRB's unit determination encompassing less than all employer’s plants, where it concluded that evidence of interaction between employees at one plant and employees at other plant did not include interaction between employees in the relevant unit category). Although some cases have analyzed this factor by considering interchange among all employees, many have focused on interchange among employees in the relevant job classification. See, e.g., Staten Island University Hosp. v. NLRB, 24 F.3d 450, 455-56 (2d Cir.1994) (registered nurses); NLRB v. Carson Cable TV, 795 F.2d 879, 885 (9th Cir.1986) (field employees).
It would be imprudent to require the NLRB to determine the composition of all units in resolving whether the Montefiore complex skilled maintenance employees should be included with the Presbyterian complex skilled maintenance employees. Likewise, we would be unwise to force the NLRB to choose either eight or forty units for UPMC by requiring that the NLRB determine whether separate units at each of the historically independent hospitals would be appropriate or whether the composition of each unit will encompass UPMC as a whole. The NLRB has discretion to find an appropriate number of units somewhere in between these absolutes. Our approach respects the NLRB’s discretion and encourages its efforts to determine, in accordance with the command in 29 U.S.C. § 159(b), the appropriate units which will afford the employees at UPMC their fullest freedom in exercising their rights under the Act.
. The entire rulemaking record reveals that the analysis which the NLRB focused on was unit scope, not unit composition. The rule resolves many scope issues. The NLRB's position, which we accept, that its discretion to determine composition (multi-facility) issues was not affected by the rule, does not alter the value, purpose, or intent of the rule or rulemaking process. Moreover, if the NLRB intended to require employer wide units for each of the eight categories listed in the rale, then it should have given notice and taken evidence on unit composition issues, which it clearly did not. See Hanover Potato Products, Inc. v. Shalala, 989 F.2d 123, 130 n. 9 (3d Cir.1993) (purpose of notice-and-comment rule-making is to afford the public the opportunity to participate).
. "Each [unit] decision ultimately rests on the particular circumstances of that unique case.” NLRB v. Carson Cable TV, 795 F.2d 879 (9th Cir.1986).
. Otherwise, with every merger each and every pre-existing bargaining unit would automatically become a non-conforming unit, and even though the non-conforming unit could transform into a conforming unit through a self-determination election, if another merger or acquisition occurred, the unit would again be non-conforming. This problem highlights the reason why the Rule does not apply to unit composition issues.