The U.S. Supreme Court case Consolidated Rock Products Co. et al. v. Du Bois in 1940 revolved around the issue of whether California's state law, which regulated working hours for those involved in mining and quarrying operations, was unconstitutional under the Fourteenth Amendment due to its interference with interstate commerce or not. Consolidated Rock Products Company and other similar companies argued that their businesses were engaged primarily in interstate commerce; thus, they should be exempt from this state regulation as it would interfere with their business activities. However, the Supreme Court ruled against them stating that while these companies did engage significantly in interstate commerce, they also had substantial local operations where mined materials were prepared before being shipped out of state - a process subject to reasonable local regulations such as labor laws for worker safety and health reasons. Therefore, even though some aspects of their business could be considered part of an unbroken stream of interstate commerce (and hence potentially immune from certain types of state regulation), there remained significant locally-focused elements within their overall operation which justified application of California's work hour restrictions without violating constitutional principles.

In the dissenting opinion for Consolidated Rock Products Co. et al. v. Du Bois, Justice McReynolds disagreed with the majority's decision to uphold California's state law that allowed a minimum wage for women and minors in public works projects. He argued that this law was unconstitutional as it interfered with freedom of contract under the Fourteenth Amendment’s Due Process Clause, which he believed should be protected from legislative interference unless there is an overwhelming health or safety concern involved. In his view, setting a minimum wage did not meet these criteria and thus constituted an unjustifiable intrusion into private contractual relationships between employers and employees.