International Emergency Economic Powers Act (IEEPA) and Tariffs: Historical Background and Key Issues [June 5, 2019] [open pdf - 578KB]
From the Document: "President Donald J. Trump recently announced his intention to use powers granted to the President under the International Emergency Economic Powers Act (IEEPA) (50 U.S.C. §§ 1701 et seq.) to impose and gradually increase a 5% tariff on all goods imported from Mexico until 'the illegal migration crisis is alleviated through effective actions taken by Mexico.' Invoked in response to an 'unusual and extraordinary threat, which has its source in whole or substantial part outside the United States,' no President has previously used IEEPA to impose tariffs on a specific country. Using IEEPA's precursor statute, the Trading with the Enemy Act of 1917 (TWEA), however, President Nixon imposed a 10% tariff on all imports into the United States in response to a monetary crisis."
CRS Insight, IN11129
Congressional Research Service: https://crsreports.congress.gov/