In the case of Hospital Building Co. v. Trustees of Rex Hospital et al., the U.S. Supreme Court ruled that a private, non-profit hospital could be considered to be engaged in commerce and thus subject to federal antitrust laws under the Sherman Act. The court found that even though Rex Hospital did not operate for profit, it was still involved in commercial activities such as purchasing supplies and equipment, employing staff, and charging patients for services rendered - all of which affected interstate commerce either directly or indirectly. Therefore, its acquisition of another local hospital could potentially restrain trade or create a monopoly within their market area if left unchecked by antitrust law enforcement.

In the dissenting opinion for Hospital Building Co. v. Trustees of Rex Hospital, Justice William O. Douglas argued that the majority's decision to allow a private hospital to sue under antitrust laws was misguided and could have far-reaching implications on other non-profit organizations such as schools or churches. He contended that these entities should not be considered "persons" within the meaning of antitrust legislation because they do not engage in business activities with profit-making motives like traditional corporations do. Furthermore, he expressed concern about potential misuse of litigation by non-profits against their competitors which would divert resources away from their primary charitable missions and towards legal battles instead.