In the case of Federal Trade Commission v. Procter & Gamble Co., 1966, the U.S. Supreme Court ruled in favor of the FTC, affirming its decision that Procter & Gamble's acquisition of Clorox Chemical Company violated Section 7 of the Clayton Act which prohibits mergers and acquisitions where their effect may be to substantially lessen competition or tend to create a monopoly. The court found that P&G's purchase could potentially reduce competition by allowing it to leverage its already dominant position in grocery products into another market (household liquid bleach), even though there was no direct product overlap between P&G and Clorox at that time. This ruling set an important precedent for future antitrust cases as it expanded interpretation beyond just immediate competitive harm but also potential future effects on competition.

In the dissenting opinion for Federal Trade Commission v. Procter & Gamble Co., Justice Harlan argued that the majority's decision was based on speculative assumptions about potential anti-competitive effects of Procter & Gamble's acquisition of Clorox, rather than concrete evidence. He contended that there was no substantial proof to suggest that this merger would lessen competition or create a monopoly in any line of commerce. Furthermore, he criticized the majority’s reliance on an "incipiency" doctrine which allowed them to block mergers based solely on their potential future impact on competition, even when current market conditions did not support such conclusions. This approach, according to Justice Harlan, could lead to arbitrary and inconsistent enforcement of antitrust laws and discourage legitimate business growth through acquisitions.