The U.S. Supreme Court case National Labor Relations Board v. Pennsylvania Greyhound Lines, Inc., et al., 1937 revolved around the issue of whether or not an employer was in violation of the National Labor Relations Act (NLRA) for refusing to bargain with a labor union that had been selected by its employees as their representative. The Pennsylvania Greyhound Lines, Inc., argued that they were under no obligation to negotiate with the union because it included supervisors who were considered part of management according to company policy and thus ineligible for collective bargaining rights under NLRA provisions. However, the court ruled in favor of the National Labor Relations Board (NLRB), stating that while certain supervisory positions may be excluded from collective bargaining units if they fall within specific categories defined by law, this did not automatically apply to all individuals holding supervisory roles within a company. Therefore, unless it could be proven otherwise on a case-by-case basis, such employees should generally be regarded as eligible for inclusion in unions and protected by NLRA regulations.

In the dissenting opinion for the case of NATIONAL LABOR RELATIONS BOARD v. PENNSYLVANIA GREYHOUND LINES, INC., Justice McReynolds disagreed with the majority's interpretation of interstate commerce within the context of labor disputes. He argued that Pennsylvania Greyhound Lines, Inc.'s business operations were primarily intrastate in nature and thus should not be subject to federal regulation under the National Labor Relations Act (NLRA). According to him, only a small fraction of their bus routes crossed state lines and therefore did not constitute substantial enough involvement in interstate commerce to warrant NLRA jurisdiction. Furthermore, he contended that Congress had overstepped its constitutional bounds by attempting to regulate activities which are essentially local in character through an overly broad interpretation of its power over interstate commerce.