The United States v. Penn-Olin Chemical Co. case in 1963 was a significant antitrust lawsuit where the U.S government challenged a joint venture between two major chemical companies, Pennsylvania Industrial Chemical Corp (Pennsalt) and Olin Mathieson Chemical Corporation (Olin). The government argued that this collaboration would violate Section 7 of the Clayton Act by reducing competition in the sodium chlorate market within Southeastern states. Sodium Chlorate is an essential component used for bleaching paper pulp. At that time, Pennsalt was one of only three domestic manufacturers while Olin had plans to enter production independently before forming a partnership with Pennsalt instead. The Supreme Court ruled in favor of the U.S Government stating that even though no actual harm to competition occurred yet, potential future harm could arise from such collaborations as it might discourage other competitors from entering into or expanding within the market due to increased concentration and dominance by existing players.

In the dissenting opinion for United States v. Penn-Olin Chemical Co., Justice Harlan argued that the majority's decision was based on an overly broad interpretation of Section 7 of the Clayton Act, which could potentially stifle legitimate business growth and competition. He contended that a joint venture between two companies should not be considered illegal merely because it might reduce potential competition in a hypothetical market scenario. Instead, he suggested that such ventures should only be deemed unlawful if there is clear evidence to suggest they would result in monopolistic practices or significantly impede actual competition within an existing market. Furthermore, he expressed concern over how this ruling could discourage businesses from entering new markets due to fear of legal repercussions under antitrust laws.