The U.S. Supreme Court case Denver Union Stock Yard Co. v. United States et al., 1937, revolved around the issue of whether the federal government had regulatory authority over a private company's business operations that were deemed to be in public interest but not directly involved in interstate commerce. The Denver Union Stock Yard Company argued against an order by the Secretary of Agriculture setting maximum rates for its services, claiming it was unconstitutional as their business did not involve interstate commerce and thus should not fall under federal regulation. However, the Supreme Court ruled against them stating that while their direct operations might only be intrastate, they played a significant role in facilitating interstate commerce due to their position within broader supply chains and markets - hence falling under Congress' Commerce Clause powers. This decision reinforced the broad interpretation of what constitutes 'interstate commerce', allowing for increased federal oversight on businesses indirectly affecting such trade.

In the dissenting opinion for Denver Union Stock Yard Co. v. United States, Justice McReynolds disagreed with the majority's interpretation of the Packers and Stockyards Act of 1921. He argued that Congress did not intend to give such broad regulatory power over private businesses to an administrative agency like the Secretary of Agriculture. According to him, this would be a violation of constitutional principles separating powers among different branches of government as it essentially allows legislative power to be exercised by non-legislative entities. Furthermore, he contended that if Congress had intended such sweeping changes in traditional business practices and property rights, they would have made their intentions clear in legislation rather than leaving it up for judicial interpretation or bureaucratic discretion.