50 U.S.C. § 4303

It shall be unlawful— (a) For any person in the United States, except with the license of the President, granted to such person, or to the enemy, or ally of enemy, as provided in this chapter, to trade, or attempt to trade, either directly or indirectly, with, to, or from, or for, or on account of, or on behalf of, or for the benefit of, any other person, with knowledge or reasonable cause to believe that such other person is an enemy or ally of enemy, or is conducting or taking part in such trade, directly or indirectly, for, or on account of, or on behalf of, or for the benefit of, an enemy or ally of enemy. (b) For any person, except with the license of the President, to transport or attempt to transport into or from the United States, or for any owner, master, or other person in charge of a vessel of American registry to transport or attempt to transport from any place to any other place, any subject or citizen of an enemy or ally of enemy nation, with knowledge or reasonable cause to believe that the person transported or attempted to be transported is such subject or citizen. (c) For any person (other than a person in the service of the United States Government or of the Government of any nation, except that of an enemy or ally of enemy nation, and other than such persons or classes of persons as may be exempted hereunder by the President or by such person as he may direct), to send, or take out of, or bring into, or attempt to send, or take out of, or bring into the United States, any letter or other writing or tangible form of communication, except in the regular course of the mail; and it shall be unlawful for any person to send, take, or transmit, or attempt to send, take, or transmit out of the United States, any letter or other writing, book, map, plan, or other paper, picture, or any telegram, cablegram, or wireless message, or other form of communication intended for or to be delivered, directly or indirectly, to an enemy or ally of enemy: Provided, however , That any person may send, take, or transmit out of the United States anything herein forbidden if he shall first submit the same to the President, or to such officer as the President may direct, and shall obtain the license or consent of the President, under such rules and regulations, and with such exemptions, as shall be prescribed by the President. (d) Whenever, during the present war, the President shall deem that the public safety demands it, he may cause to be censored under such rules and regulations as he may from time to time establish, communications by mail, cable, radio, or other means of transmission passing between the United States and any foreign country he may from time to time specify, or which may be carried by any vessel or other means of transportation touching at any port, place, or territory of the United States and bound to or from any foreign country. Any person who willfully evades or attempts to evade the submission of any such communication to such censorship or willfully uses or attempts to use any code or other device for the purpose of concealing from such censorship the intended meaning of such communication shall be punished as provided in section 4315 of this title .