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22 U.S. Code § 454 - Unlawful use of the American flag by vessel of foreign state

It shall be unlawful for any vessel belonging to or operating under the jurisdiction of any foreign state to use the flag of the United States thereon, or to make use of any distinctive signs or markings, indicating that the same is an American vessel.
Any vessel violating the provisions of subsection (a) of this section shall be denied for a period of three months the right to enter the ports or territorial waters of the United States except in cases of force majeure.
(Nov. 4, 1939, ch. 2, § 14, 54 Stat. 11.)