Over the dissents of conservative Justices Clarence Thomas and Samuel Alito, the emergency decision prevents authorities from removing the migrants under the Alien Enemies Act of 1798 as a legal challenge proceeds, a win for the American Civil Liberties Union (ACLU), which is suing on the migrants’ behalf.

But the justices declined the ACLU’s additional request to leapfrog the lower courts to immediately take up the issue of whether President Trump can invoke the rarely used law outside of wartime.

“Today’s ruling effectively extends the temporary freeze that the justices put on Alien Enemies Act removals from the Northern District of Texas back on April 19,” said Steve Vladeck, CNN Supreme Court analyst and professor at Georgetown Law. “Because lower courts have blocked use of the act in every other district in which the president has sought to invoke it, that means it’s effectively pausing all removals under the act until the 5th Circuit – and, presumably, the Supreme Court itself – conclusively resolves whether they’re legal and how much process is due if so.”

The high court acted in an emergency appeal from the American Civil Liberties Union contending that immigration authorities appeared to be moving to restart removals under the Alien Enemies Act of 1798. The Supreme Court had said earlier in April that deportations could proceed only if those about to be removed had a chance to argue their case in court and were given “a reasonable time” to contest their pending removals.