In Turner vs. Flanigan et al., the Supreme Court of the United States ruled that a state court cannot issue an injunction to prevent a federal officer from performing their duties under federal law. The case arose when William H. Turner, who was appointed by President James Buchanan as Collector of Customs for the Port of Mobile in Alabama, attempted to take possession of his office and perform his official duties but was prevented from doing so by an injunction issued by an Alabama state court at the request of John W. Flanigan and other individuals claiming title to certain property located within said port district which they alleged belonged to them or their assignees. The Supreme Court held that since Congress had exclusive authority over customs collection districts, it could not be interfered with or impeded in any way by state courts through injunctions or otherwise; thus, such action taken against Turner violated both Article VI Clause 2 (the Supremacy Clause) and Section 914 of Title 28 U.S Code (which provides for immunity from suit).

In Turner v. Flanigan et al., the Supreme Court was asked to decide whether a state court had jurisdiction over an action brought by a citizen of another state against citizens of the same state in which it sat. The majority opinion held that such jurisdiction did not exist, as it would be contrary to the spirit and letter of Article III, Section 2, Clause 1 of the United States Constitution. Justice Grier dissented from this decision on two grounds: firstly, he argued that Congress had given express authority for states to exercise such jurisdiction; secondly, he contended that even if Congress had not done so explicitly then they should have been impliedly allowed to do so under their sovereign powers granted by Article IV Section 4. He further noted that there was no evidence or precedent indicating any intention on behalf of Congress or anyone else to limit these rights and thus concluded with his belief that "the right is too plain for argument".