The Interstate Commerce Commission v. Mechling case in 1946 revolved around the issue of whether a barge line was required to file its rates with the Interstate Commerce Commission (ICC) under the provisions of the Interstate Commerce Act. A.L. Mechling Barge Line, a private carrier by water, had been transporting grain without filing its rates with ICC as it believed that it was exempt from such requirements due to being classified as a 'private carrier'. However, ICC argued that since Mechling held itself out to serve indifferently all customers for compensation and thus operated functionally as a common carrier rather than private one, it should be subject to regulations applicable for common carriers including rate filing requirement. The U.S Supreme Court ruled in favor of ICC stating that even though legally defined as 'private', if an entity operates practically like a 'common' carrier serving general public indiscriminately for profit then they must comply with rules set forth by ICC which includes submitting their freight charges or tariffs.

In the dissenting opinion for Interstate Commerce Commission v. Mechling, Justice Frankfurter disagreed with the majority's interpretation of the Interstate Commerce Act. He argued that Congress intended to give the ICC broad authority to regulate all forms of interstate transportation and prevent discriminatory practices. The majority's decision, he believed, undermined this intent by allowing barge operators like Mechling to charge lower rates than railroads without proving they were not engaging in unfair competition or discrimination against other modes of transport. This could potentially destabilize competitive balance among different types of carriers and harm public interest in a fair and efficient transportation system.