The Cement Manufacturers Protective Association v. United States case in 1924 revolved around the Sherman Antitrust Act, which prohibits certain business activities that federal government regulators deem to be anti-competitive. The Cement Manufacturers Protective Association and several individual cement companies were charged with violating this act by colluding to fix prices and divide markets among themselves. They argued that their actions did not constitute interstate commerce, thus falling outside the scope of the Sherman Act. However, the Supreme Court disagreed with this argument stating that while manufacturing itself is not a part of interstate commerce, any conspiracies or agreements formed during production intending to restrain trade would affect such commerce significantly enough for it to fall under federal jurisdiction as per the Sherman Act's provisions. Therefore, these manufacturers' practices were deemed illegal because they restrained competition unlawfully.

In the dissenting opinion for Cement Manufacturers Protective Association v. United States, Justice McReynolds disagreed with the majority's interpretation of the Sherman Act and its application to price-fixing agreements among competitors. He argued that such agreements should not be considered illegal per se under antitrust law unless they unreasonably restrain trade or commerce. In his view, a more nuanced analysis was necessary to determine whether an agreement actually had harmful effects on competition rather than simply assuming harm based on its nature as a price-fixing agreement. Furthermore, he expressed concern about potential negative implications of broad interpretations of antitrust laws for business practices and economic stability in general.