In the case of Vaca et al. v. Sipes, Administrator (1966), the United States Supreme Court addressed a dispute between an employee and his union over representation in a grievance procedure against his employer. The court held that when a labor union has been given exclusive power to represent all employees in collective bargaining and grievance adjustment processes, it also has a duty to fairly represent each member during these procedures. This means that unions cannot arbitrarily ignore or process grievances, showing hostility or discrimination towards certain members. However, if the individual can prove bad faith conduct by their union representative during this process they may have grounds for legal action against both their employer and their union under Section 301(a) of Labor Management Relations Act (LMRA). In this particular case though, there was no evidence found suggesting such misconduct from the Union's side.

In the dissenting opinion for VACA et al. v. SIPES, Justice Harlan disagreed with the majority's view that a union could be held liable for breaching its duty of fair representation if it arbitrarily ignored or weakly processed a grievance. He argued that this expanded interpretation of the National Labor Relations Act was not supported by legislative history and would unduly burden unions with litigation risks from disgruntled members who were unhappy with how their grievances were handled. Furthermore, he contended that such an approach might discourage unions from settling disputes informally due to fear of potential lawsuits, thus undermining labor-management relations overall.