15 U.S. Code § 77 - Discrimination against neutral Americans in time of war
Whenever, during the existence of a war in which the United States is not engaged, the President shall be satisfied that there is reasonable ground to believe that any vessel, American or foreign, is, on account of the laws, regulations, or practices of a belligerent Government, making or giving any undue or unreasonable preference or advantage in any respect whatsoever to any particular person, company, firm, or corporation, or any particular description of traffic in the United States or its possessions or to any citizens of the United States residing in neutral countries abroad, or is subjecting any particular person, company, firm, or corporation or any particular description of traffic in the United States or its possessions, or any citizens of the United States residing in neutral countries abroad to any undue or unreasonable prejudice, disadvantage, injury, or discrimination in regard to accepting, receiving, transporting, or delivering, or refusing to accept, receive, transfer, or deliver any cargo, freight, or passengers, or in any other respect whatsoever, he is authorized and empowered to direct the detention of such vessels by withholding clearance or by formal notice forbidding departure, and to revoke, modify, or renew any such direction.
Whenever, during the existence of a war in which the United States is not engaged, the President shall be satisfied that there is reasonable ground to believe that under the laws, regulations, or practices of any belligerent country or Government, American ships or American citizens are not accorded any of the facilities of commerce which the vessels or citizens of that belligerent country enjoy in the United States or its possessions, or are not accorded by such belligerent equal privileges or facilities of trade with vessels or citizens of any nationality other than that of such belligerent, the President is authorized and empowered to withhold clearance from one or more vessels of such belligerent country until such belligerent shall restore to such American vessels and American citizens reciprocal liberty of commerce and equal facilities of trade; or the President may direct that similar privileges and facilities, if any, enjoyed by vessels or citizens of such belligerent in the United States or its possessions be refused to vessels or citizens of such belligerent; and in such case he shall make proclamation of his direction, stating the facilities and privileges which shall be refused, and the belligerent to whose vessels or citizens they are to be refused, and thereafter the furnishing of such prohibited privileges and facilities to any vessel or citizen of the belligerent named in such proclamation shall be unlawful; and he may change, modify, revoke, or renew such proclamation; and any person or persons who shall furnish or attempt or conspire to furnish or be concerned in furnishing or in the concealment of furnishing facilities or privileges to ships or persons contrary to the prohibition in such proclamation shall be liable to a fine of not less than $2,000 nor more than $50,000 or to imprisonment not to exceed two years, or both, in the discretion of the court.
In case any vessel which is detained by virtue of this subchapter shall depart or attempt to depart from the jurisdiction of the United States without clearance or other lawful authority, the owner or master or person or persons having charge or command of such vessel shall be severally liable to a fine of not less than $2,000 nor more than $10,000, or to imprisonment not to exceed two years, or both, and in addition such vessel shall be forfeited to the United States.
The President of the United States is authorized and empowered to employ such part of the land or naval forces of the United States as shall be necessary to carry out the purposes of this subchapter.