(dissenting, with whom Ireland, J., joins). I agree with the court that G. L. c. 150E, § 7 (a) (§ 7 [a]), bars public employers and public employees from entering into a collective bargaining agreement (CBA) with a stated term of more than *166three years. But the court today expands the scope of this statutory term limit to preclude the contracting parties from including in their CBA a provision, namely an “evergreen clause,” that the court itself agrees is intended to serve as “a continuing code of conduct while parties negotiate a new bargaining agreement.” Ante at 163. Section 7 (a) contains no direct prohibition against such a provision in a three-year CBA. In reaching its construction of § 7 (a), the court turns its back on the reasonable interpretation that the Labor Relations Commission (now division of labor relations [division])1 has followed for decades, finding consistency between an evergreen clause and the provisions of § 7 (a); public sector employers and unions, including the parties to the present case, have long relied on that interpretation. The court also, in my view, ignores “the unique nature of the employer-employee relationship in the public sector,” Massachusetts Org. of State Eng’rs & Scientists v. Labor Relations Comm’n, 389 Mass. 920, 927 (1983), and the special public policy considerations that animate it. I disagree with the court’s interpretation of § 7 (a), and therefore respectfully dissent.
1. Although the court recites the background facts of this case, it is useful to highlight some of them to provide context to the questions of statutory interpretation at issue.2 For more than thirty years — since at least 1978 — the CBAs between the Boston Housing Authority (BHA) and the National Conference of Firemen and Oilers, Local 3 (Local 3), have had a stated term of between two and three years,* ***3 and have contained an identically worded clause, the evergreen clause, providing that “[d]uring any period of negotiations between the parties hereto, the provisions *167of this Agreement shall remain in full force and effect until such time as a new agreement has been signed. Such negotiations will be conducted in good faith.”4
The parties’ most recent CBA, namely, the memorandum of agreement (MOA), had a stated term from April 1, 2001, to March 31, 2004. After Local 3 gave notice in January, 2004, of its intent to negotiate a new CBA, the parties met in negotiation sessions nine times, until April, 2006, without reaching agreement. In the meantime, the parties continued to operate under the provisions of the 2001-2004 MOA, and there is no indication the BHA suggested in those negotiating sessions that the MOA’s provisions were no longer in effect. Rather, in connection with these negotiations, one of the BHA’s proposals for the new CBA was to eliminate the evergreen clause, but Local 3 did not agree. In late January, 2006, in response to what it deemed a fiscal crisis, the BHA notified Local 3 that it intended to lay off all sixteen firemen covered by the minimum staffing provision in Attachment A to the MOA. The BHA met with Local 3 three times over the layoffs, with each side offering one or more counter-proposals that were not accepted by the other. Then, based on the stated reasons of lack of need for the firemen and fiscal issues, the BHA unilaterally implemented the layoffs. It was in responding to Local 3’s 2006 grievance over the firemen’s termination that the BHA first asserted its claim that there was no CBA in effect between the parties after March 31, 2004, because the evergreen clause contravened § 7 (a), and therefore the BHA was not obligated to honor the minimum staffing provision in the MOA’s Attachment A.
2. The pertinent language in § 7 (a) is the following: “Any collective bargaining agreement reached between the employer and the exclusive representative shall not exceed a term of three years.” The court states that this language is clear, and goes on to conclude — by employing the oft-repeated rubric of statutory interpretation that where the words of a statute are clear, the “[language] is conclusive as to the intent of the Legislature,” and the court will not look to extrinsic sources — that the *168evergreen clause in the MOA was unenforceable because it violated “the unambiguous language of G. L. c. 150E, § 7 (a).” Ante at 162. While I agree that the language of § 7 (a) provides clarity on the point that parties to a CBA may not contract for longer than three years, the language itself does not lead to the conclusion drawn by the court. Rather, the section is silent on the question whether a limit on the length of a contract precludes the enforcement of an evergreen clause.
Section 7 (a) is part of G. L. c. 150E, a comprehensive statutory scheme regulating public employee collective bargaining. See Keane v. City Auditor of Boston, 380 Mass. 201, 208 (1980). Its meaning deserves to be considered in a broader context than the court has provided. “[T]ime and again we have stated that we should not accept the literal meaning of the words of a statute without regard for that statute’s purpose and history.” Commerce Ins. Co. v. Commissioner of Ins., 447 Mass. 478, 481 (2006), quoting Sterilite Corp. v. Continental Cas. Co., 397 Mass. 837, 839 (1986). Citing the division’s decision in Town of Burlington, 3 M.L.C. 1440 (1977), the court essentially adopts the division’s articulation of the purposes served by § 7 (a): to give employees the ability to choose new bargaining representatives every three years, and protect the employer and incumbent union from too-frequent elections5; to require reassessment by the parties of the CBA at least once every three years; and to “prevent!] a governing body from unduly tying the hands of its successors.” Town of Burlington, 3 M.L.C. at 1441. See ante at *169163. The court, however, summarily rejects the conclusion articulated by the division in its Town of Burlington decision, that an evergreen clause is consistent with these statutory purposes, and does not violate the three-year term provision in § 7 (a).
We have long recognized that the division, the State agency charged with the responsibility of implementing G. L. c. 150E, see G. L. c. 23, § 9R, has specialized knowledge and expertise in labor relations, and, as a result, its decisions are entitled to substantial deference. See Worcester v. Labor Relations Comm’n, 438 Mass. 177, 180 (2002); Boston Police Superior Officers Fed’n v. Labor Relations Comm’n, 410 Mass. 890, 892 (1991); Quincy City Hosp. v. Labor Relations Comm’n, 400 Mass. 745, 748-749 (1987); Boston Teachers Union, Local 66 v. Boston, 44 Mass. App. Ct. 746, 752 (1998). Such deference is particularly appropriate where, as here, “statutory lacunae exist.” Middleborough v. Housing Appeals Comm., 449 Mass. 514, 523 (2007) (where there is statutory gap, agency charged with administration of statute is to spell out details of legislative policy).
As just mentioned, the division has upheld the validity of evergreen clauses under § 7 (a), and has done so consistently since 1977. See Town of Burlington, 3 M.L.C. at 1441. See, e.g., Massachusetts Coalition of Police, AFL-CIO, Local 170, 16 M.L.C. 1630, 1632 n.3 (1990). In Town of Burlington, the division explained that an evergreen clause is consistent with the statutory language regarding contract terms of three years because the clause merely provides a “mechanism and procedure to be followed prior to the execution of a successor agreement.” Town of Burlington, supra at 1441.
Resting on its view that the statutory language is “unambiguous [],” the court simply states that the division’s previous determinations that an evergreen clause is not inconsistent with § 7 (a) are “not controlling.” Ante at 164. I disagree. For a number of reasons, including that an evergreen clause may or may not become operable at the end of a CBA — it only takes effect in the circumstance where the parties have not reached a new agreement at the end of the original contract term and remain in good faith negotiations to do so; and that an evergreen clause merely allows the provisions of a CBA to continue to govern relations between parties during an interim period of *170negotiations, culminating in either a new agreement or impasse, I am persuaded that there is no inherent inconsistency between an evergreen clause and § 7 (a). In my view, the division’s interpretation of § 7 (a) is a reasonable one to which this court should defer.6
While the court rejects the parties’ evergreen clause — and by extension, all evergreen clauses — it points to a provision in G. L. c. 150E, § 9, that authorizes parties to a CBA to extend the contract “by mutual agreement for a period of time in excess of the aforementioned time.” In the court’s view, this statutory provision is in accordance with § 7 (a), because, the court states, it authorizes parties, after a CBA has expired, to enter into “a subsequent agreement extending the prior terms and conditions of their agreement, thereby maintaining the status quo while negotiations for a new CBA are ongoing.” Ante at 164-165. Considered as a whole, G. L. c. 150E, § 9, offers more support for the validity of an evergreen clause than for its rejection. Section 9 provides a detailed set of procedures — including mediation, fact finding, and arbitration — that parties to a public sector CBA may seek to activate when one or more of them believe they have reached impasse in negotiating over the terms of the agreement. The section does not require that the parties’ CBA have ended before its provisions may be invoked, and — to put the portion of § 9 quoted by the court in context — the statute expressly states that when a petition is filed under its provisions
“for a determination of an impasse following negotiations for a successor agreement, an employer shall not implement *171unilateral changes until the collective bargaining process, including mediation, fact finding or arbitration, if applicable, shall have been completed and the terms and conditions of employment shall continue in effect until the collective bargaining process, including mediation, factfinding or arbitration, if applicable, shall have been completed; provided, however, that nothing contained herein shall prohibit the parties from extending the terms and conditions of such a collective bargaining agreement by mutual agreement for a period of time in excess of the aforementioned time” (emphasis added).
G. L. c. 150E, § 9, ninth par.
Parties to a CBA engaged in negotiating the terms of a successor agreement are not required to follow the procedural regime set out in G. L. c. 150E, § 9, and I recognize that “the terms and conditions” of a CBA may encompass something less than every provision of the agreement. But the important point is that § 9 recognizes the need to maintain the status quo and provide for continuity while negotiations over a new CBA are ongoing, without waiting until the old agreement has expired and the parties are left in limbo. That, of course, is also the purpose of the evergreen clause.7 As a matter of policy, the evergreen clause, like the quoted provisions of G. L. c. 150E, § 9, avoid “uncontracted-for gaps of time between bargaining agreements,” Gustafson v. Wachusett Regional Sch. Dist., 64 Mass. App. Ct. 802, 809-810 n.11 (2005), and “[foster] labor peace by providing a continuing code of conduct while a new agreement is under negotiation.” Town of Burlington, 3 M.L.C. at 1441. Moreover, keeping in mind the strong policy in favor of collective bargaining between public employers and employees, see, e.g., Somerville v. Somerville Mun. Employees Ass’n, 451 Mass. 493, 496 (2008), it bears emphasis that the evergreen clause included in the MOA here was the result of mutual bargaining, whereby the parties offered consideration and at least one party likely compromised or otherwise made a concession to obtain the inclusion of the clause.
*172When interpreting § 7 (a) in relation to the evergreen clause, these types of public policy considerations should be weighed in the balance. This court and the Appeals Court have recognized the special nature of collective bargaining in the public sector, where employees are not permitted to strike but perform services important to the public. See Gustafson v. Wachusett Regional Sch. Dist., 64 Mass. App. Ct. at 809-810 n.11. Cf. Local 589, Amalgamated Transit Union v. Massachusetts Bay Transp. Auth., 414 Mass. 323, 326-327 (1993).8 Cf. also Massachusetts Org. of State Eng’rs & Scientists v. Labor Relations Comm’n, 389 Mass. 920, 927 (1983); Boston Teachers Union, Local 66 v. Boston, 44 Mass. App. Ct. at 754-755. The court, however, does not undertake any evaluation of these concerns. Nor does it consider the implication that its decision will have on the settled expectation of public sector employees and employers that evergreen clauses tied to the negotiation of a new agreement are permissible. Its failure to do so not only ignores our precedent, but may well have unfortunate consequences for employers, employees, and the public arising from uncertainty *173after the stated term of a CBA has been reached and a new CBA is not yet in place.
3. Underlying the court’s opinion is a wholly legitimate concern about the seemingly leisurely status and pace of public sector bargaining. I agree that successor CBAs between public sector employers and employees should be negotiated and executed on a timetable that makes them truly successive, rather than retroactively effective. At the same time, it is clear from the record, and from our own decisions, see, e.g., National Ass’n of Gov’t Employees v. Commonwealth, 419 Mass. 448, cert, denied, 515 U.S. 1161 (1995), that this has not always been the practice or perhaps even the norm, and yet there has been no legislative effort to change it. The court’s insistence that the language of § 7 (a) unambiguously invalidates an evergreen clause is belied by this history. Furthermore, in the present case, the BHA had options available to it to end the extension of the MOA as well as the evergreen clause, if that is what it sought.9
For these reasons, I respectfully dissent. I would conclude, as did the Superior Court judge, that the arbitrator’s award did not violate § 7 (a) and was not subject to vacation pursuant to G. L. c. 150C, § 11 (a) (3), on that ground. Because I also believe that the judge below correctly decided, contrary to the BHA’s arguments, that the award does not violate any well-defined public policy and is not otherwise illegal — two issues not reached by the court here — I would affirm the judgment of the Superior Court.
The Labor Relations Commission has been subsumed into the division of labor relations of the Department of Labor (division).
These facts are taken from those found by the arbitrator, supplemented by undisputed information in the record.
The affidavit of Thomas Brassil, who served as business agent for Local 3 from 1978 to October, 2001, includes a chart reflecting the stated terms of each collective bargaining agreement (CBA) in effect between the BHA and Local 3 from 1978 to the present, and also the time period the provisions of each CBA remained in effect. The first CBA listed, with an execution date of May 24, 1979, had a stated term that went from October 1, 1978, to May 31, 1982, more than three years. All the other contracts had stated terms for three or fewer years. There is no explanation provided for the longer term of the first contract, but it appears to be an anomaly.
As the court states, with respect to the 2001-2004 memorandum of agreement (MOA) between the parties, the arbitrator found that it incorporated the evergreen clause contained in the parties’ 1998-2001 CBA. See ante at 159.
There is some legislative history to support this first purpose. In the legislation enacting G. L. c. 150E, see St. 1973, c. 1078, the Legislature made clear that it was directly replacing sections of the prior public sector collective bargaining law, G. L. c. 149, §§ 178D, 178F-178N, with the new chapter. See St. 1973, c. 1078, §§ 1, 2. As Local 3 points out, the prior law did not contain any language limiting the durational term of CBAs, but did contain a “contract bar” provision expressly prohibiting any election of a new union to become the exclusive bargaining representative of public employees during the term of an existing CBA. See G. L. c. 149, § 178H (3), as amended by St. 1967, c. 746. The three-year term in § 7 (a) of the new G. L. c. 150E ensured that new elections could take place within a reasonable time period — three years — and thereby served the interests of all parties. The division has determined that evergreen clauses are consistent with this purpose, because the clauses do not preclude representation elections every three years. See, e.g., Brockton Sch. Comm., 4 M.L.C. 1005, 1007 (1977); University of Mass., 2 M.L.C. 1001, 1004 (1975); City of Somerville, 1 M.L.C. 1312, 1314 (1975).
In the circumstances of this case, the court’s focus on the “unambiguous[]” nature of § 7 (a) is misleading. As indicated in the text, the words used by the Legislature may be clear as far as they go, but the issue here concerns a point on which the statute is silent. As to that point, the fact that for more than thirty years, the agency has adopted a construction of § 7 (a) that differs from the court’s by itself indicates that the statute is not so clear when applied to the particular question we are considering. See New England Med. Ctr. Hosp., Inc. v. Commissioner of Revenue, 381 Mass. 748, 750 (1980), quoting Hutton v. Phillips, 45 Del. 156, 160 (1949) (statute unambiguous if “virtually anyone competent to understand it, and desiring fairly and impartially to ascertain its signification, would attribute to the expression in its context a meaning such as the one we derive, rather than any other; and would consider any different meaning, by comparison, strained, or far-fetched, or unusual, or unlikely”).
The parties are subject to the requirement of good faith bargaining under the explicit terms of the evergreen clause. Accordingly, one party is prevented from indefinitely stalling negotiations simply because it benefited from the terms of the prior agreement that was being preserved by the evergreen clause.
In Local 589, Amalgamated Transit Union v. Massachusetts Bay Transp. Auth., 414 Mass. 323 (1993), this court discussed a “rollover” provision in a CBA between the Massachusetts Bay Transportation Authority (MBTA) and its employees, which stated that the provisions of the CBA “shall continue in force ‘from year to year thereafter unless changed by the parties.’ ” Id. at 326. Finding the “rollover” provision to be valid, this court concluded that the MBTA could not terminate unilaterally the CBA simply by giving notice. Id. at 326-327. The court wrote: “Where a strike would be unlawful, or at least arguably so, and arbitration is mandated for the ultimate resolution of disputes concerning the terms of a collective bargaining agreement. . . and where the public interest in uninterrupted mass transit service is great, public policy supports the enforcement of the collective bargaining agreement as written and the rejection of any implication that the right to terminate it on reasonable notice in the circumstances of this case. By its terms, the collective bargaining agreement is still in effect.” Id. at 327. The court states that the Local 589 decision is “inapposite” here because the MBTA is not covered by G. L. c. 150E, and therefore not subject to § 7 (a). Ante at 164. While it is true that § 7 (a) does not apply to the MBTA, the same public policy concerns do apply with equal force in the present case. According to art. VTH of the CBA between the BHA and Local 3, the BHA’s employees — like all other public employees, see G. L. c. 150E, § 9A (a) — are not permitted to strike, arbitration has been contractually mandated for resolution of grievances under all their CBAs, and there is a strong public interest in having the operation and maintenance of public housing developments take place without disruption caused by labor unrest.
If the BHA were to conclude that Local 3 was not bargaining in good faith concerning the extension of the MOA (or a change in the evergreen clause), it could file an unfair labor practice charge pursuant to G. L. c. 150E, § 10 (b) (2), or a grievance under the MOA. A determination of bad faith bargaining in either forum, by itself, would render void the evergreen clause. Furthermore, assuming the parties continued to bargain in good faith, nothing in the evergreen clause interfered with the ability of the BHA to declare an impasse — on its own and with no resort to the procedures laid out in G. L. c. 150E, § 9 — after exhausting the possibility of reaching agreement. See Newton Branch of the Mass. Police Ass’n v. Newton, 396 Mass. 186, 190 (1985); Massachusetts Org. of State Eng’rs & Scientists v. Labor Relations Comm'n, 389 Mass. 920, 926-928 (1983). If the BHA were to follow such a path, it would be free to implement unilaterally those changes that were “reasonably comprehended within its pre-impasse proposals.” Id. at 927, quoting Hanson Sch. Comm., 5 M.L.C. 1671, 1675-1676 (1979). Accord Newton Branch of the Mass. Police Ass’n v. Newton, supra.