In Leloup v. Port of Mobile, the Supreme Court of the United States was asked to decide whether a state could impose a tax on goods imported from another state. The case arose when the Port of Mobile, Alabama, imposed a tax on goods imported from Louisiana. The plaintiff, Leloup, argued that the tax was unconstitutional because it violated the Commerce Clause of the United States Constitution. The Supreme Court held that the tax was unconstitutional because it violated the Commerce Clause. The Court reasoned that the tax was a burden on interstate commerce and was therefore prohibited by the Commerce Clause. The Court also noted that the tax was discriminatory because it only applied to goods imported from Louisiana, and not to goods imported from other states. The Court concluded that the tax was unconstitutional and struck it down. This decision established the principle that states cannot impose taxes on goods imported from other states, as such taxes are a burden on interstate commerce and are prohibited by the Commerce Clause.

In Leloup v. Port of Mobile, the Supreme Court was tasked with determining whether a state-created corporation could be sued in federal court without its consent. The majority opinion held that such suits were not permissible under the Eleventh Amendment and thus dismissed the case. In dissent, Justice Field argued that Congress had granted federal courts jurisdiction over cases involving foreign citizens suing states or their agents for damages caused by tortious acts committed within those states' borders. He further noted that this power to grant jurisdiction extended to corporations created by a state as well as individuals acting on behalf of it, and therefore concluded that suit against the Port of Mobile should have been allowed to proceed in federal court despite its status as an arm of Alabama's government.