The United States v. Penn-Olin Chemical Co. case in 1967 revolved around an antitrust issue where the U.S government accused two major chemical companies, Pennsylvania Salt Manufacturing Company and Olin Mathieson Chemical Corporation, of violating Section 7 of the Clayton Act. The two firms had formed a joint venture named Penn-Olin to produce sodium chlorate in the Southeastern region of America, which was seen as potentially reducing competition within this market sector. The Supreme Court ruled that potential competition could be considered under Section 7 and thus held that forming Penn-Olin would indeed violate it because both parent companies were capable individually of entering into direct competition with each other in the production and sale of sodium chlorate.

In the dissenting opinion for the United States v. Penn-Olin Chemical Co., it was argued that there was insufficient evidence to prove a violation of Section 7 of the Clayton Act, which prohibits mergers and acquisitions where their effect may be significantly to lessen competition or tend towards monopoly. The dissenting justices contended that mere potentiality or possibility is not enough to establish such an effect; rather, there must be clear proof showing reasonable probability of substantial lessening in competition due to merger activities. They also noted that both companies were already engaged in producing sodium chlorate separately before they decided on joint production, thus making it difficult to argue convincingly about any significant reduction in competition resulting from their collaboration. Furthermore, they pointed out inconsistencies and lack of clarity within majority's reasoning regarding market definition and competitive effects analysis.