“The Alien Enemies Act of 1798 is a wartime authority that allows the president to detain or deport the natives and citizens of an enemy nation. The law permits the president to target these immigrants without a hearing and based only on their country of birth or citizenship. Although the law was enacted to prevent foreign espionage and sabotage in wartime, it can be — and has been — wielded against immigrants who have done nothing wrong, have evinced no signs of disloyalty, and are lawfully present in the United States.”
Famously, the Alien Enemies Act was last invoked for Japanese internment during WWII.