In the case of Magnesium Casting Co. v. National Labor Relations Board (1970), the U.S Supreme Court ruled in favor of the National Labor Relations Board (NLRB). The dispute arose when Magnesium Casting Company refused to bargain with a labor union that had been certified by NLRB as the exclusive representative for its employees, arguing that some votes were cast by ineligible voters and thus, it was not properly elected. However, NLRB rejected this claim and ordered the company to negotiate with the union. When taken to court, Justice Thurgood Marshall delivered an unanimous decision stating that if a company refuses to comply with an order from NLRB on grounds which they could have raised during certification proceedings but did not do so until after certification was granted, then such objections cannot be entertained later in enforcement proceedings unless there are extraordinary circumstances - which were absent in this case.

In the dissenting opinion for Magnesium Casting Co. v. National Labor Relations Board, Justice Hugo Black disagreed with the majority's ruling that an employer violated federal labor law by refusing to bargain collectively with a union over pension and insurance benefits of retired employees. He argued that Congress did not intend for employers to be required to negotiate about matters concerning individuals who are no longer part of the workforce when it enacted the National Labor Relations Act (NLRA). According to him, retirees do not fall within NLRA’s definition of “employee” as they have permanently ceased work and thus cannot engage in concerted activities for mutual aid or protection regarding their employment conditions. Furthermore, he contended that if Congress had intended such a significant departure from traditional concepts of collective bargaining, it would have explicitly stated so in clear language within NLRA itself rather than leaving this important matter open-ended or ambiguous.