A federal judge issued an order temporarily blocking the Trump administration from using the Alien Enemies Act of 1798 on Saturday, preventing the administration from using the wartime act to remove Venezuelan illegal immigrants who were believed to be members of the Tren de Aragua gang.

U.S. District Judge James Boasberg ordered a pause in deportations under Trump’s proclamation for 14 days while he considers whether the use of the AEA was illegal. He also demanded the immediate return of planes that were already headed to Central America.

The ruling came in response to a lawsuit filed by Democracy Forward and the ACLU challenging the use of the rarely-invoked wartime act that is meant to be used to resist a foreign invasion. The law allows the government to arrest, detain and deport illegal immigrants who are older than 14 and come from countries threatening an “invasion or predatory incursion” of the U.S.

Attorneys for Democracy Forward and the ACLU argue the Alien Enemies Act has only ever been invoked during wartime, as in the War of 1812, World War I and World War II. 

“I think there’s clearly irreparable harm here given these folks will be deported,” Boasberg, an Obama appointee, said at a virtual hearing on Saturday. 

“Any plane containing these folks that is going to take off or is in the air needs to be returned to the United States however that is accomplished,” Boasberg announced. “Make sure it’s complied with immediately.”

Boasberg raised questions about the legality of Trump using the AEA by labeling Tren de Aragua the equivalent of a foreign government.

“I find and declare that TdA is perpetrating, attempting, and threatening an invasion or predatory incursion against the territory of the United States,” Trump wrote in his declaration.

Those who meet the description outline in the order “are subject to immediate apprehension, detention, and removal.” 

Trump’s order directed Attorney General Pam Bondi to sign a letter within 60 days making the declaration U.S. policy.

The Trump administration has appealed Boasberg’s order to the D.C. Circuit Court of Appeals.

The president’s declaration is an example of him following through on his campaign promise to use the Alien Enemies Act as one method to help him carry out mass deportations.

Last month, he also designated Tren de Aragua and seven other Latin American cartels as foreign terrorist organizations.