We granted certiorari to clarify the standard that governs a claim that a union has breached its duty of fair representation in its negotiation of a back-to-work agreement terminating a strike. We hold that the rule announced in Vaca v. Sipes, 386 U.S. 171, 190, 87 S.Ct. 903, 916, 17 L.Ed.2d 842 (1967)-that a union breaches its duty of fair representation if its actions are either "arbitrary, discriminatory, or in bad faith"-applies to all union activity, including contract negotiation. We further hold that a union's actions are arbitrary only if, in light of the factual and legal landscape at the time of the union's actions, the union's behavior is so far outside a "wide range of reasonableness," Ford Motor Co. v. Huffman, 345 U.S. 330, 338, 73 S.Ct. 681, 686, 97 L.Ed. 1048 (1953), as to be irrational.
* This case arose out of a bitter confrontation between Continental Airlines, Inc. (Continental), and the union representing its pilots, the Air Line Pilots Association, International (ALPA). On September 24, 1983, Continental filed a petition for reorganization under Chapter 11 of the Bankruptcy Code. Immediately thereafter, with the approval of the Bankruptcy Court, Continental repudiated its collective-bargaining agreement with ALPA and unilaterally reduced its pilots' salaries and benefits by more than half. ALPA responded by calling a strike that lasted for over two years. See 886 F.2d 1438, 1440 (CA5 1989).
Of the approximately 2,000 pilots employed by Continental, all but about 200 supported the strike. By the time the strike ended, about 400 strikers had "crossed over" and been accepted for reemployment in order of reapplication. App. to Brief for Continental Airlines, Inc., as Amicus Curiae A11, and n. 8. By trimming its operations and hiring about 1,000 replacements, Continental was able to continue in business. By August 1985, there were 1,600 working pilots and only 1,000 strikers. 886 F.2d, at 1440.
The strike was acrimonious, punctuated by incidents of violence and the filing of a variety of law suits, charges, and countercharges. In August 1985, Continental notified ALPA that it was withdrawing recognition of ALPA as the collective-bargaining agent for its pilots. ALPA responded with a federal lawsuit alleging that Continental was unlawfully refusing to continue negotiations for a new collective-bargaining agreement. In this adversary context, on September 9, 1985, Continental posted its "Supplementary Base Vacancy Bid 1985-5" (85-5 bid)-an act that precipitated not only an end to the strike, but also the litigation that is now before us. Ibid.
For many years Continental had used a "system bid" procedure for assigning pilots to new positions. Bids were typically posted well in advance in order to allow time for necessary training without interfering with current service. When a group of vacancies was posted, any pilot could submit a bid specifying his or her preferred position (captain, first officer, or second officer), base of operations, and aircraft type. Ibid. In the past, vacant positions had been awarded on the basis of seniority, determined by the date the pilot first flew for Continental. The 85-5 bid covered an unusually large number of anticipated vacancies-441 future captain and first officer positions and an undetermined number of second officer vacancies. Pilots were given nine days-until September 18, 1985-to submit their bids. Id., at 1441.
Fearing that this bid might effectively lock the striking pilots out of jobs for the indefinite future, ALPA authorized the strikers to submit bids. Several hundred did so, as did several hundred working pilots. Although Continental initially accepted bids from both groups, it soon became concerned about the bona fides of the striking pilots' offers to return to work at a future date. It therefore challenged the strikers' bids in court and announced that all of the 85-5 bid positions had been awarded to working pilots. Ibid.
At this juncture, ALPA intensified its negotiations for a complete settlement. ALPA's negotiating committee and Continental reached an agreement, which was entered as an order by the Bankruptcy Court on October 31, 1985. See App. 7-41. The agreement provided for an end to the strike, the disposition of all pending litigation, and reallocation of the positions covered by the 85-5 bid. See id., at 10-34.