The U.S. Supreme Court case United States v. First City National Bank of Houston et al., 1966, centered around the Clayton Act's anti-trust provisions and their application to banking mergers. The government challenged a merger between two Texas banks - the First City National Bank of Houston and Republic National Bank of Dallas - arguing that it would significantly reduce competition in commercial banking in violation of Section 7 of the Clayton Act. The defendants argued that because they operated in different geographic markets, there was no substantial competition between them to be lessened or restrained by their merger. However, the Supreme Court ruled against this argument stating that potential competition could also be considered under Section 7; even if two companies are not currently competing due to geographical separation, a merger can still violate antitrust laws if it prevents future direct competition from occurring within those regions. Therefore, despite operating separately at present time, both banks had plans for expansion which would have led them into each other’s territories creating potential competitors.

In the dissenting opinion for the United States v. First City National Bank of Houston case, it was argued that the majority's decision to block a merger between two banks on antitrust grounds was misguided. The dissenters believed that banking is not an ordinary business and should not be subjected to traditional antitrust laws in the same way as other industries. They pointed out that banks are heavily regulated by both state and federal authorities, which already prevents them from engaging in monopolistic practices. Furthermore, they contended that allowing mergers can actually enhance competition by enabling smaller banks to compete with larger ones more effectively. Therefore, they disagreed with the majority's view that this particular merger would have anti-competitive effects.