In the United States v. New York, New Haven & Hartford Railroad Co., 1957 case, the Supreme Court ruled in favor of the U.S. government against a railroad company for violating antitrust laws. The issue at hand was whether or not a merger between two railroads would create an unlawful monopoly and stifle competition within their shared market area. The court found that this proposed merger did indeed violate Section 7 of the Clayton Act which prohibits mergers and acquisitions where the effect may be to substantially lessen competition or tend to create a monopoly. This ruling set important precedent for future cases involving potential monopolies created by business mergers.

In the dissenting opinion for United States v. New York, New Haven & Hartford Railroad Co., Justice Harlan argued that the Interstate Commerce Commission (ICC) had overstepped its authority by ordering a merger without considering whether it was in line with public interest or not. He contended that such an action was beyond the scope of ICC's powers as defined by Congress and violated principles of administrative law. Furthermore, he expressed concern about potential negative impacts on competition within the railroad industry due to this decision. In his view, allowing mergers without thorough examination could lead to monopolistic practices and harm consumers' interests in terms of pricing and service quality.