Administration officials said they expect the fight over using the wartime act to ultimately head to the Supreme Court.

The Alien Enemies Act of 1798 gives the president wartime powers to deport undocumented immigrants with little to no due process.

More than half of the 261 immigrants expelled to El Salvador on Saturday were swept out of the United States using a wartime powers act, a White House official said Sunday, amid questions about whether the Trump administration flouted a judge’s order barring use of the statute to hasten deportations.