The U.S. Supreme Court case American Trucking Associations, Inc., et al. v. United States et al., 1957 revolved around the issue of whether or not the Interstate Commerce Commission (ICC) had overstepped its authority in regulating contract carriers as if they were common carriers under Part II of the Motor Carrier Act, 1935. The plaintiffs, a group of trucking companies represented by American Trucking Associations, argued that this was an abuse of power and violated their rights to due process under the Fifth Amendment. However, after reviewing previous court decisions and considering legislative intent behind relevant laws such as Transportation Act of 1940 and Administrative Procedure Act (APA), the Supreme Court ruled against them in a unanimous decision stating that ICC's actions were within its statutory powers granted by Congress to ensure fair competition among different types of motor carriers while protecting public interest.

In the dissenting opinion for American Trucking Associations, Inc., et al. v. United States et al., Justice Brennan disagreed with the majority's interpretation of the Interstate Commerce Act and its application to contract carriers. He argued that Congress intended to create a clear distinction between common carriers and contract carriers, which was not reflected in the majority's ruling. According to him, this differentiation was crucial because it determined whether or not certain regulatory provisions applied - specifically those related to rates and practices of common carriers versus those applicable only to contract ones. The justice believed that by blurring these lines, the court had overstepped its boundaries into legislative territory by effectively rewriting parts of an act passed by Congress rather than interpreting them as they were meant when enacted.