In the case of Pyramid Motor Freight Corp. v. Ispass et al., 1946, the United States Supreme Court ruled in favor of Pyramid Motor Freight Corporation, overturning a decision by the National Labor Relations Board (NLRB). The NLRB had previously found that Pyramid violated labor laws when it fired two employees for their union activities. However, upon review, the Supreme Court determined that there was insufficient evidence to prove that these terminations were motivated by anti-union sentiment or actions on behalf of the employer. Instead, they concluded that one employee was dismissed due to his poor work performance and another because he lied about his reasons for missing work during an investigation into alleged misconduct at a company party. Therefore, this ruling established important precedent regarding burden of proof in cases involving allegations of unfair labor practices.

In the dissenting opinion for Pyramid Motor Freight Corp. v. Ispass, Justice Frankfurter disagreed with the majority's interpretation of Section 7(a) of the National Labor Relations Act (NLRA). He argued that this section should not be interpreted to mean that employees have an absolute right to engage in union activities during working hours without employer consent. Instead, he believed it was intended to prevent employers from interfering with or restraining employees' rights to self-organize and bargain collectively outside work hours. Furthermore, he contended that allowing such activities during work time would disrupt business operations and potentially harm other workers who do not wish to participate in these activities. Therefore, according to Justice Frankfurter’s view, while employers cannot discriminate against employees based on their union membership or activity outside work hours under NLRA Section 8(3), they can regulate conduct at workplace within reasonable limits.