In the case of United States v. American Building Maintenance Industries, 1974, the U.S Supreme Court addressed an antitrust dispute involving a merger between two companies that provided building maintenance services. The government argued that this merger violated Section 7 of the Clayton Act as it would substantially lessen competition or tend to create a monopoly in certain markets for janitorial and cleaning services. However, the court ruled against them stating there was insufficient evidence to prove these allegations. The court found no clear proof showing that either company had dominated their respective markets before merging or were likely to do so after merging. It also noted that both firms faced significant competition from other businesses within their market areas which further undermined claims of potential monopolization. Furthermore, while acknowledging concerns over possible anti-competitive effects resulting from mergers among large corporations generally, Justice Thurgood Marshall writing for majority stated such fears alone could not justify blocking every merger involving big companies without concrete evidence demonstrating probable harm to competition. This ruling clarified standards needed when assessing potential anti-competitive impacts under Section 7 of Clayton Act and underscored importance of providing substantial evidentiary support when alleging violations under this law.

The dissenting opinion in the case of United States v. American Building Maintenance Industries argued that the majority's decision to uphold a lower court ruling, which found ABM guilty of violating antitrust laws, was incorrect. The dissenters believed that there was insufficient evidence to prove that ABM had engaged in predatory pricing or attempted monopolization. They also disagreed with the majority's interpretation and application of Section 2 of the Sherman Act, arguing it should not be used as broadly as it was by their colleagues. Furthermore, they felt that this broad interpretation could potentially harm competition rather than protect it by discouraging aggressive competitive strategies often employed by smaller companies trying to gain market share from larger competitors.