The United States Supreme Court case, United States v. Michigan Portland Cement Company, revolved around the interpretation of a tariff act from 1909. The Michigan Portland Cement Company imported cement clinker (a component used in making cement) and argued that it should be classified under the "cement" category for import duties purposes. However, the U.S government contended that it should fall under a different classification with higher rates as per the Tariff Act of 1909. The court ruled in favor of the government stating that while technically clinker could be considered as an unfinished form of cement, its state at time of import was not usable as is and required further processing to become actual cement; thus justifying its separate categorization attracting higher tariffs.

The dissenting opinion in the case of United States v. Michigan Portland Cement Company argued that the majority's decision was inconsistent with previous rulings and interpretations of the Sherman Act. The dissenters believed that there was sufficient evidence to prove a violation of antitrust laws, as it appeared that cement manufacturers had conspired to fix prices and restrict competition. They disagreed with the majority's view that these actions were merely parallel conduct or coincidental similarities between companies' business strategies, rather than an illegal agreement or conspiracy. Furthermore, they contended that this ruling could potentially undermine future enforcement efforts against price-fixing conspiracies by setting a higher standard for proof than what has been traditionally required under antitrust law.