In the case of Carnegie Steel Company v. United States in 1915, the U.S Supreme Court ruled that a merger between several steel and iron companies was illegal under the Sherman Antitrust Act. The court found that these companies had formed a trust to control competition and create a monopoly in the steel industry, which violated federal law. This decision marked one of many during this era where courts were actively enforcing antitrust laws to break up large corporations and trusts deemed harmful to competitive markets. The ruling against Carnegie Steel Company underscored the government's commitment towards maintaining fair business practices by preventing monopolies from dominating industries.

The dissenting opinion in the case of Carnegie Steel Company v. United States argued that the majority's decision to dissolve the United States Steel Corporation as a monopoly under the Sherman Antitrust Act was incorrect. The dissenters believed that just because a corporation has gained significant market share, it does not automatically mean they are suppressing competition or creating a monopoly. They pointed out that U.S. Steel had actually increased production and reduced prices, which is beneficial for consumers and indicative of healthy competition rather than monopolistic behavior. Furthermore, they contended that if every large corporation were considered a potential monopoly simply due to their size or success, this could discourage businesses from growing and innovating for fear of legal repercussions.