The Trading with the Enemy Act is an American law forbidding trade with enemies in times of war. The official description of the Act, as part of Public Law, is "An Act To define, regulate, and punish trading with the enemy, and for other purposes."
The law was passed by the United States Congress on October 6, 1917 in order to prevent American citizens from doing business with the German Empire, a nation with which the United States was at war.
The law has subsequently been applied to the Axis Powers, Cuba under Fidel Castro, Iraq under Saddam Hussein, and others. One of the most famous applications of the law was the seizure of the Union Banking Corporation by the American government in October 1942, on the basis that it was a Nazi "front group". The Union Banking Corporation was operated by Prescott Bush.
More recently, it has been used by the Department of Justice to prosecute "Human shields" who travelled to Iraq in advance of the 2003 invasion on the basis that they spent money while in Iraq to act as human shields.
There have been accusations that Dick Cheney violated the Trading with the Enemy Act when a subsidiary of Halliburton Corporation opened an office in Tehran, Iran while Cheney was CEO of that company.
President Bill Clinton pardoned Marc Rich in his last days as President. One of the crimes for which Clinton pardoned Rich was a violation of the Trading with the Enemy Act — for trading in oil with Iran during the Iran Hostage Crisis.
The Act is Public Law 65-91, 65th Congress, Session I, Chapters 105, 106, October 6, 1917.