In the case of United States v. First National Bank & Trust Co. of Lexington et al., 1963, the U.S. Supreme Court ruled on a dispute involving antitrust laws and bank mergers. The government had sought to prevent a merger between two Kentucky banks - First National Bank & Trust Company and Second National Bank & Trust Company - arguing that it would significantly reduce competition in violation of Section 7 of the Clayton Act, an antitrust law designed to promote business competition and prevent monopolies. The District Court initially dismissed this claim, stating that banking was not considered "commerce" under the terms of this act; therefore, it did not apply in this situation. However, upon appeal by the government, the Supreme Court reversed this decision with a unanimous vote. The court held that banking is indeed commerce as defined by federal law because banks engage in numerous commercial activities such as lending money or facilitating transactions across state lines which have direct effects on interstate commerce. Therefore they are subject to federal regulation including antitrust laws like Section 7 of Clayton Act.

In the dissenting opinion for United States v. First National Bank & Trust Co. of Lexington et al., Justice Harlan disagreed with the majority's view that a bank merger violated Section 7 of the Clayton Act, which prohibits acquisitions that may lessen competition or create a monopoly. He argued that this interpretation was too broad and did not take into account other factors such as market realities and banking regulations in place at state level to prevent anti-competitive behavior. Furthermore, he believed it was inappropriate to apply antitrust laws designed for industrial companies to banks without considering their unique characteristics and regulatory environment. In his view, this approach could potentially hinder necessary consolidation within the banking industry rather than promoting competition.