Southern Pacific Co. v. Arizona

Congress is authorized, under Article 1, Section 8, Clause 3, of the Constitution, "to regulate Commerce with foreign Nations, and among several States, and with the Indian Tribes." This is the Commerce Clause, the basis for a number of Supreme Court challenges involving alleged attempts by individuals, companies, or--in the case of Southern Pacific Co. v. Arizona--states to impede the flow of interstate commerce.

"Commerce," as defined by the Constitution, has a very broad meaning. The term encompasses any sort of business or commercial exchange and all interstate communication via telephone, telegraph, radio, or other electronic means. In addition, it refers to all interstate travel, whether for business or for personal reasons.

States have control over their intrastate commerce, but interstate commerce is completely under federal control. This provision was designed to prevent competition between states with seaports and those without and to help to preserve the doctrine of federalism in the operation of the country's internal affairs.