In the 1947 case United States v. National City Lines, Inc., et al., the U.S. Supreme Court addressed allegations of conspiracy to monopolize interstate commerce against several major corporations including General Motors and Firestone Tire. The defendants were accused of colluding to acquire control over a number of transit companies, forming a transportation monopoly that violated Section 1 and 2 of the Sherman Antitrust Act. They allegedly replaced electric streetcar systems with buses in order to sell more petroleum products and rubber tires, an event known as "the Great American Streetcar Scandal." The court found these corporations guilty on one count: conspiring to monopolize sales of buses and supplies to local transit companies; however, they were acquitted on two other counts related to attempts at monopolizing transportation services themselves. Each corporation was fined $5,000 while each corporate officer involved was fined $1 - penalties criticized for their leniency given the scale of profits made from this scheme.

The dissenting opinion in the United States v. National City Lines, Inc., et al., 1947 case argued that the majority's decision was based on a misinterpretation of the Sherman Act. The dissenters believed that there was insufficient evidence to prove that the defendants had conspired to monopolize any part of interstate commerce or restrain trade unlawfully. They contended that acquiring control over local transit companies and replacing their equipment with buses did not constitute an illegal restraint of trade or attempt to monopolize under antitrust laws; rather, it represented legitimate business practices within a competitive market economy. Furthermore, they pointed out inconsistencies in how lower courts had applied these laws previously and expressed concern about potential negative impacts on future business transactions if such activities were deemed unlawful without clear proof of intent to harm competition.