In the United States v. E.I. Du Pont De Nemours & Co., 1956, the U.S Supreme Court ruled that DuPont's acquisition of a significant share in General Motors (GM) violated antitrust laws as it resulted in an illegal concentration of market power. The court found that although GM and DuPont were not direct competitors, their close relationship could potentially stifle competition within the automobile industry by discouraging other suppliers from competing for GM’s business or encouraging preferential treatment towards products produced by companies owned or controlled by DuPont. This ruling expanded on previous interpretations of Section 7 of the Clayton Act to include not only horizontal mergers between direct competitors but also vertical mergers where one company acquires another at a different level in the supply chain.

In the dissenting opinion for United States v. E.I. Du Pont De Nemours & Co., Justice Reed argued that the majority's decision to break up DuPont's ownership of General Motors (GM) stock was based on a misinterpretation of antitrust laws and an overreach by the court into business affairs. He contended that there was no evidence presented showing any actual restraint or monopolization in violation of Sherman Act, nor did it demonstrate intent to do so in future. The mere size or potential power due to stock ownership should not be considered as anti-competitive behavior without concrete proof of abuse or misuse leading towards monopoly control, he asserted. Furthermore, he pointed out that this ruling could have far-reaching implications for other companies with similar investment structures and warned against judicial intrusion into corporate matters best left to Congress' discretion.