The United States v. Pabst Brewing Co. case in 1965 revolved around the acquisition of Blatz Brewing Company by Pabst Brewing Company, which was challenged by the U.S government under Section 7 of the Clayton Act, alleging it would lessen competition or create a monopoly in certain beer markets. The Supreme Court ruled that even though there were many other competitors within these markets and no immediate threat to competition could be seen, potential harm to competition should also be considered when evaluating mergers and acquisitions. Therefore, they held that this merger did violate antitrust laws because it had the potential to negatively impact competitive conditions in future scenarios despite not having an immediate effect on market concentration levels at present times.

In the dissenting opinion for United States v. Pabst Brewing Co., Justice Harlan argued that the majority's decision to reverse and remand was based on a misinterpretation of Section 7 of the Clayton Act, which prohibits acquisitions that may substantially lessen competition or tend to create a monopoly. He contended that there was no substantial evidence showing such an effect from Pabst's acquisition of Blatz. The lower court had found no reasonable probability of these anti-competitive effects occurring in any relevant market, and this finding should have been upheld by the Supreme Court according to standard review principles. Furthermore, he criticized the majority for not providing clear guidance as to what constitutes "probable" anticompetitive effects under Section 7, leaving businesses uncertain about when their mergers might be deemed illegal.