The Supreme Court case Louisville & Nashville Railroad Company v. United States in 1924 revolved around the issue of whether a railroad company could be compelled to provide free transportation for federal prohibition agents under an old statute that required railroads to transport U.S mail and its guards without charge. The Louisville & Nashville Railroad Company argued that this law did not extend to Prohibition agents, as they were not postal employees or mail guards. However, the government contended otherwise, stating that these agents were entitled to free passage while performing their duties related to enforcing Prohibition laws. The Supreme Court ruled in favor of the United States government, holding that federal prohibition officers fell within the scope of "guards" mentioned in the statute and thus should be transported freely by railroads when carrying out their official duties. This decision was based on a broad interpretation of what constituted 'mails' and 'guards', which included any person employed by Post Office Department who is engaged on trains where mails are carried.

In the dissenting opinion for Louisville & Nashville Railroad Company v. United States, it was argued that the Interstate Commerce Commission (ICC) had overstepped its authority by imposing a rate increase on railroads without sufficient evidence to justify such an action. The dissenters believed that while the ICC has broad powers to regulate interstate commerce, these powers should not be exercised arbitrarily or capriciously. They contended that there must be substantial evidence of a need for increased rates before they can be imposed and in this case, no such evidence existed. Furthermore, they asserted that if left unchecked, this decision could set a dangerous precedent where regulatory bodies could impose their will upon industries with little justification or oversight.