A federal judge barred the Trump administration Saturday from carrying out deportations under a sweeping 18th century law that the president invoked hours earlier to speed removal of Venezuelan gang members from the United States.

U.S. District Judge James E. Boasberg said he needed to issue his order immediately because the government already was flying migrants it claimed were newly deportable under President Donald Trump’s proclamation to be incarcerated in El Salvador and Honduras, AP reported. 

El Salvador already agreed this week to take up to 300 migrants that the Trump administration designated as gang members.

“I do not believe I can wait any longer and am required to act,” Boasberg said during a Saturday evening hearing in a lawsuit brought by the ACLU and Democracy Forward. “A brief delay in their removal does not cause the government any harm,” he added, noting they remain in government custody but ordering that any planes in the air be turned around.

The ruling came hours after Trump claimed the Venezuelan gang Tren de Aragua was invading the United States and invoked the Alien Enemies Act of 1798, a wartime authority that allows the president broader leeway on policy and executive action to speed up mass deportations.

The act has only ever been used three times before, all during wars. Its most recent application was during World War II, when it was used to incarcerate Germans and Italians as well as for the mass internment of Japanese-American civilians.

In a proclamation released just over an hour before Boasberg’s hearing, Trump contended that Tren de Aragua was effectively at war with the United States.