50 U.S.C. § 205

Whenever the President, in pursuance of the provisions of this chapter, has called forth the militia to suppress combinations against the laws of the United States, and to cause the laws to be duly executed, and the insurgents shall have failed to disperse by the time directed by the President, and when the insurgents claim to act under the authority of any State or States, and such claim is not disclaimed or repudiated by the persons exercising the functions of government in such State or States, or in the part or parts thereof in which such combination exists, and such insurrection is not suppressed by such State or States, or whenever the inhabitants of any State or part thereof are at any time found by the President to be in insurrection against the United States, the President may, by proclamation, declare that the inhabitants of such State, or of any section or part thereof where such insurrection exists, are in a state of insurrection against the United States; and thereupon all commercial intercourse by and between the same and the citizens thereof and the citizens of the rest of the United States shall cease and be unlawful so long as such condition of hostility shall continue; and all goods and chattels, wares and merchandise, coming from such State or section into the other parts of the United States, or proceeding from other parts of the United States to such State or section, by land or water, shall, together with the vessel or vehicle conveying the same, or conveying persons to or from such State or section, be forfeited to the United States.