In the case of Air Line Pilots Association, International v. Joseph E. O'Neill et al., 1990, the U.S Supreme Court ruled that a union could be held liable for breaching its duty of fair representation if it intentionally discriminated against some members in favor of others without a legitimate reason. The dispute arose when Eastern Airlines pilots who were on strike were replaced by non-striking pilots and new hires represented by the same union (Air Line Pilots Association). When Eastern filed for bankruptcy and was bought out by another airline, jobs were scarce and preference was given to non-strikers over strikers based on an agreement between the Union and new owners. Striking pilots sued their union alleging breach of duty due to discriminatory conduct favoring one set of employees over another without justification. The court sided with striking pilots stating that unions must represent all members fairly regardless of personal views or affiliations.

In the dissenting opinion for AIR LINE PILOTS ASSOCIATION, INTERNATIONAL v. JOSEPH E. O'NEILL et al., Justice Blackmun argued that the majority misinterpreted the Railway Labor Act (RLA) and its application to this case. He contended that under RLA, a union is not required to represent all employees equally in every situation but must only avoid discrimination 'invidious' in nature - meaning it should not be arbitrary or based on race, creed, or color. In this case involving Eastern Airline pilots who crossed picket lines during a strike and were later penalized by their union, he believed there was no such discrimination as they knowingly took risks when crossing those lines. Furthermore, he pointed out that allowing courts to interfere with internal disciplinary actions of unions could undermine labor relations stability which RLA aims to promote.