In the National Labor Relations Board v. Mackay Radio & Telegraph Co., 1937, the U.S. Supreme Court ruled in favor of Mackay Radio & Telegraph Company. The case revolved around a labor dispute where workers had gone on strike and were subsequently replaced by their employer, Mackay Radio & Telegraph Company. When the strike ended, some of these replacement workers kept their jobs while others did not get rehired due to alleged anti-union bias from management. The National Labor Relations Board (NLRB) argued that this was an unfair labor practice under Section 8(1) and (3) of the National Labor Relations Act because it interfered with employees' rights to engage in concerted activities for mutual aid or protection. However, the Supreme Court held that employers have no legal obligation to discharge replacements so as to reinstate striking employees after a strike ends unless there is evidence showing discrimination against union members or other unlawful practices involved in retaining replacements over strikers. The court also established what came to be known as "Mackay Doctrine," which states that although it's illegal for companies to fire striking workers simply because they went on strike; however, those who are permanently replaced during a lawful economic strike do not have an absolute right to reinstatement when they offer unconditionally return-to-work post-strike.

In the dissenting opinion for the National Labor Relations Board v. Mackay Radio & Telegraph Co., Justice Black argued that employers should not have an unrestricted right to replace striking workers, particularly when a strike is provoked by unfair labor practices. He contended that such a ruling undermines the purpose of the National Labor Relations Act (NLRA), which aims to equalize bargaining power between employers and employees. The majority's interpretation, according to him, would allow companies to punish strikers and discourage union activities by permanently replacing them. This could potentially lead to more industrial unrest and conflict rather than promoting peaceful negotiation and settlement as intended by NLRA.