with whom The Chief Justice and Justice Scalia join, dissenting.
The Idaho Supreme Court held that summary judgment was improper and that Tharon Rawson and the other respondents could proceed to trial against the United Steelworkers of America (Union) on a state-law tort theory. Although the respondents have not yet established liability under Idaho law, the Union argues that federal law must govern and bar their suit. To support this position, the Union relies on both §301 of the Labor Management Relations Act, 29 U. S. C. § 185(a), and the duty of fair represen*377tation implicit in §9(a) of the National Labor Relations Act (NLRA), 49 Stat. 453, as amended, 29 U. S. C. § 159(a). The Court accepts the Union’s contentions with respect to §301 and does not reach the issue of pre-emption by the duty of fair representation. With all respect, I dissent. Neither of the Union’s arguments for displacing Idaho law without any trial on the merits has validity.
I
The Union bases its §301 argument on our decisions m Lingle v. Norge Division of Magic Chef, Inc., 486 U. S. 399, 405-406 (1988); Electrical Workers v. Hechler, 481 U. S. 851, 854 (1987); and Allis-Chalmers Corp. v. Lueck, 471 U. S. 202, 211 (1985). These cases hold that § 301 pre-empts state-law causes of action that require interpretation of a collective-bargaining agreement. In my view, they have no application here. The Idaho Supreme Court, whose determination of state law supersedes that of the trial court, has declared that the respondents’ case rests on allegations of the Union’s active negligence in a voluntary undertaking, not its contractual obligations.
Adopting verbatim a standard from the Restatement (Second) of Torts § 323 (1965), the Idaho Court expressed the law governing the respondents’ claims as follows:
“ ‘One who undertakes, gratuitously or for consideration, to render services to another which he should recognize as necessary for the protection of the other’s person or things, is subject to liability to the other for physical harm resulting from his failure to exercise reasonable care to perform his undertaking, if
“‘(a) his failure to exercise such care increases the risk of harm, [or]
“ ‘(b) the harm is suffered because of the other’s reliance upon the undertaking.’” Rawson v. United Steelworkers of America, 111 Idaho 630, 637, 726 P. 2d 742, 749 (1986).
*378According to the Idaho Supreme Court’s second opinion, the respondents, can prove the elements of the tort described in §323 without relying on the Union’s collective-bargaining agreement. The Court states:
“In the instant case, we are not faced with looking at the Collective Bargaining Agreement to determine whether it imposes some new duty upon the union— rather it is conceded the union undertook to inspect and, thus, the issue is solely whether that inspection was negligently performed under traditional Idaho tort law.” 115 Idaho 785, 787, 770 P. 2d 794, 796 (1989).
Placing this analysis of state law in the context of our precedents, the Idaho court explains:
“[T]he instant case is clearly distinguishable from Heckler in that here the state tort basis of the action was not abandoned, but has been pursued consistently both at the trial and appellate levels and the tort exists without reference to the collective bargaining agreement.” Id., at 787-788, 770 P. 2d, at 796-797.
The court states further:
“[As in Lingle v. Norge Division of Magic Chef, Inc., supra], no interpretation of the collective-bargaining agreement is required to determine whether the union member of the inspection team committed a tort when he committed various acts and omissions such as failure to note the self-rescuers were stored in boxes with padlocks or that the activating valves of the oxygen-breathing-apparatuses were corroded shut. Rather, such alleged acts of negligence are measured by state tort law.” Id., at 788, 770 P. 2d, at 797.
These statements reveal that the Idaho Supreme Court understood the federal pre-emption standards and interpreted state law not to implicate them. Because we have no basis for disputing the construction of state law by a state supreme court, see Clemons v. Mississippi, 494 U. S. 738, 747 *379(1990), I submit that, at this stage of the proceedings, we must conclude that § 301 does not govern the respondents’ claims.
The Court reaches a different conclusion because it doubts that the Idaho Supreme Court means what it seems to have said. The Court bases its view, to a large extent, on the Idaho court’s expressed intention to “adhere to [its first] opinion as written.” 115 Idaho, at 788, 770 P. 2d, at 797. The first opinion says: “Because the union, pursuant to the provisions of the collective bargaining agreement, had contracted to inspect and in fact, inspected the mine, it owed the (minimal) duty to its members to exercise due care in inspecting and in reporting the findings of its inspection.” 111 Idaho, at 638, 726 P. 2d, at 750. The Court construes the remark to negate the unequivocal statements quoted above. I cannot accept this labored interpretation.
The Idaho Supreme Court’s adherence to the first opinion does not implicate § 301 because it does not require interpretation of a collective-bargaining agreement. The first opinion suggests that the respondents may refer to the collective-bargaining agreement. It does not eliminate the possibility, identified three times in the second opinion, that the respondents may prove the elements of § 323 without relying on the collective-bargaining agreement. Even the Union concedes:
“After Heckler, as we understand matters, both plaintiffs and the Idaho court would locate the source of the union’s duty to inspect [in a non-negligent manner] in the union’s action of accompanying company and state inspectors on inspections of the mine, and not in any contractual agreement by the union to inspect.” Brief for Petitioner 27-28.
The Court, thus, reads too much into the last sentence of the Idaho Supreme Court’s second opinion.
I see no reason not to allow this case to go forward with a simple mandate: The respondents may press their state claims so long as they do not rest upon the collective-bargaining *380agreement. To the extent that any misunderstanding might exist, this approach would preserve all federal interests. If the Idaho Supreme Court, after a trial on the merits, were to uphold a verdict resting on the Union’s obligations under the collective-bargaining agreement, we could reverse its decision. But for now we must take the case as the Idaho Supreme Court has given it to us. According to the second opinion, the respondents may prove the elements of §323 without relying on the Union’s contractual duties.
The Court also rules against the respondents because it surmises that § 323 has no general applicability. The Court assumes that only union members could recover from the Union for its negligence in inspecting the mine and that union members could not recover from anyone else for comparable negligence. See ante, at-370-371. I agree that a State cannot circumvent our decisions in Lingle, Hechler, and Allis-Chalmers, by the mere “relabeling” as a tort claim an action that in law is based upon the collective-bargaining process. Allis-Chalmers, 471 U. S., at 211. We must have the ultimate responsibility for deciding whether a state law depends on a collective-bargaining agreement for the purposes of § 301. In this case, however, I see no indication that the tort theory pressed by the respondents has the limited application presumed by the Court.
The Idaho Supreme Court did not invent, for the purposes of this case, the theory underlying the respondents’ claims. As Cardozo put it: “It is ancient learning that one who assumes to act, even though gratuitously, may thereby become subject to the duty of acting carefully, if he acts at all.” Glanzer v. Shepard, 233 N. Y. 236, 239, 135 N. E. 275, 276 (1922). Restatement § 323, upon which the Idaho Court relies, embodies this principle and long has guided the interpretation of Idaho tort law. See, e. g., Steiner Corp. v. American District Telegraph, 106 Idaho 787, 791, 683 P. 2d 435, 439 (1984) (fire alarm failure); S. H. Kress & Co. v. Godman, 95 Idaho 614, 616, 515 P. 2d 561, 563 (1973) (boiler explosion); *381Fagundes v. State, 116 Idaho 173, 176, 774 P. 2d 343, 346 (App. 1989) (helicopter crash); Carroll v. United Steelworkers of America, 107 Idaho 717, 723, 692 P. 2d 361, 367 (1984) (Bistline, J., dissenting) (machinery accident). The Court has identified no basis for its assumption that § 323 has a narrower scope than its plain language and these cases indicate. I thus would not find pre-emption on the mere supposition that the Union’s duty runs only to the union members.
II
The Union also argues that the duty of fair representation immunizes it from liability under § 323. Allowing the States to impose tort liability on labor organizations, it contends, would upset the balance of rights and duties that federal law has struck between unions and their members. I disagree because nothing in the NLRA supports the Union’s position.
Section 9(a) of the NLRA, 29 U. S. C. § 159(a), grants a duly elected union the exclusive authority to represent all employees in a collective-bargaining unit. We have reasoned:
“The fair interpretation of the statutory language is that the organization chosen to represent a craft is chosen to represent all its members, the majority as well as the minority, and it is to act for and not against those whom it represents. It is a principle of general application that the exercise of a granted power to act in behalf of others involves the assumption toward them of a duty to exercise the power in their interest and behalf, and that such a grant of power will not be deemed to dispense with all duty toward those from whom it is exercised unless so expressed.” Steele v. Louisville & Nashville R. Co., 323 U. S. 192, 202 (1944) (footnote omitted) (interpretation of § 2(a) of the Railway Labor Act, 45 U. S. C. § 152 (1982 ed.), adopted for § 9(a) of the NLRA in Ford Motor Co. v. Huffman, 345 U. S. 330, 337 (1953)).
*382As a result, we have read § 9(a) to establish a duty of fair representation requiring a union “to serve the interests of all members without hostility or discrimination toward any, to exercise its discretion with complete good faith and honesty, and to avoid arbitrary conduct.” Vaca v. Sipes, 386 U. S. 171, 177 (1967).
Although we have inferred that Congress intended to impose a duty of fair representation in § 9(a), I see no justification for the further conclusion that Congress desired to grant unions an immunity from all state tort law. Nothing about a union’s status as the exclusive representative of a bargaining unit creates a need to exempt it from general duties to exercise due care to avoid injuring others. At least to some extent, therefore, I would conclude that Congress “by silence indicate[d] a purpose to let state regulation be imposed.” Retail Clerks v. Schermerhorn, 375 U. S. 96, 104 (1963).
Our decision in Farmer v. Carpenters, 430 U. S. 290 (1977), confirms this view. Farmer held that the NLRA did not pre-empt a union member’s action against his union for intentional infliction of emotional distress. See id., at 305. The union member complained that his union ridiculed him in public and refused to refer jobs to him in accordance with hiring hall rules. See id., at 293. In analyzing this claim, we ruled that the NLRA’s pre-emption of state tort law depends on two factors: “the state interests in regulating the conduct in question and the potential for interference with the federal regulatory scheme. ” Id., at 297. Both of these factors militated against pre-emption in Farmer. Noting that “our cases consistently have recognized the historic state interest in ‘such traditionally local matters as public safety and order,”’ id., at 299 (quoting Allen-Bradley Local v. Wisconsin Employment Relations Bd., 315 U. S. 740, 749 (1942)), we ruled that the tort law addressed proper matters of state concern. We further observed that, although the tort liability for intentional infliction of emotional distress might interfere with the federal prohibition against discrimination by a *383union, that “potential for interference is insufficient to counterbalance the legitimate and substantial interest of the State in protecting its citizens.” 430 U. S., at 304.
The Farmer analysis reveals that Idaho may hold the union liable for negligence in inspecting the mine. The strength and legitimacy of the State’s interests in mine safety stand beyond question; the Union’s failure to exercise due care, according to the allegations, caused or contributed to the deaths of 91 Idaho miners. Allowing this case to proceed to trial, moreover, would pose little threat to the federal regulatory scheme. State courts long have held unions liable for personal injuries under state law. See, e. g., DiLuzio v. United Electrical, Radio, and Machine Workers of America, 386 Mass. 314, 318, 435 N. E. 2d 1027, 1030 (1982) (assault at workplace); Brawner v. Sanders, 244 Ore. 302, 307, 417 P. 2d 1009, 1012 (1966) (in banc) (personal injuries); Marshall v. International Longshoremen’s and Warehousemen’s Union, 57 Cal. 2d 781, 787, 371 P. 2d 987, 991 (1962) (stumble in union hall parking lot); Inglis v. Operating Engineers Local Union No. 12, 58 Cal. 2d 269, 270, 373 P. 2d 467, 468 (1962) (assault at union meeting); Hulahan v. Sheehan, 522 S. W. 2d 134, 139-141 (Mo. App. 1975) (slip and fall on union hall stairs). The Union presents no argument that this longstanding practice has interfered with federal labor regulation. Indeed, as the Court itself holds, nothing in the federal statutory scheme addresses the Union’s conduct or provides redress for the injuries that it may have produced. See ante, at 373-375.
The Union’s position also deviates from the well-established position of the Courts of Appeals. These courts have found pre-emption by the duty of fair representation in two situations. First, the courts have said that the duty of fair fair representation pre-empts state duties that depend on a collective-bargaining agreement or on the union’s status as the exclusive collective bargaining agent. See, e. g., Richardson v. United Steelworkers of America, 864 F. 2d 1162, *3841165-1167 (CA5 1989); Condon v. Local 2944, United Steelworkers of America, 683 F. 2d 590, 595 (CA1 1982). As noted above, however, the Union’s duties in this case do not stem from a contract or from its status as a union. Second, other courts have found the federal duty of fair representation to supplant equivalent state-law duties. See, e. g., Jones v. Truck Drivers Local Union No. 299, 838 F. 2d 856, 861 (CA6 1988) (sex discrimination); Maynard v. Revere Copper Products, 773 F. 2d 733, 735 (CA6 1985) (handicapped discrimination); Peterson v. Air Line Pilots Assn., International, 759 F. 2d 1161, 1170 (CA4 1985) (blacklisting). In this case, state law differs from federal law in that the duty of fair representation does not address the conduct in question. The Union, as a result, has shown no support for its contention that the duty of fair representation pre-empts the Idaho tort law. For these reasons, I dissent.