In the case of Diamond Coal and Coke Co. v. United States in 1913, the Supreme Court ruled that a coal company was not exempt from paying taxes on its own railroad tracks used for transporting its product to market. The court held that even though the rail lines were owned by the coal company and only used for their business purposes, they still constituted "property" under federal law and thus could be taxed accordingly. This decision clarified how property tax laws applied to businesses using their own infrastructure for commercial activities.

In the dissenting opinion for Diamond Coal and Coke Co. v. United States, it was argued that the Sherman Act should not apply to labor unions as they are not combinations in restraint of trade or commerce among several states. The dissenting justices believed that a union's primary purpose is to protect its members' interests, which does not inherently involve controlling production or prices in an industry across state lines - key elements of what constitutes a violation under the Sherman Act. They also pointed out that applying this act to labor unions could potentially criminalize any concerted action by employees seeking better working conditions or wages, which would be contrary to public policy and principles of justice and fairness.