A federal judge on Saturday ordered the Trump administration to cease use of an obscure wartime law to deport Venezuelans without a hearing, saying that any planes that had departed the United States with immigrants under the law needed to return.

As of early Sunday morning, it was unclear whether any such planes had departed or returned.

On Saturday, the administration published an executive order invoking the law, the Alien Enemies Act of 1798, to target Venezuelan gang members in the United States.

But shortly after the announcement, James E. Boasberg, a federal judge in Washington, D.C., said he would issue a temporary order blocking the government from deporting any immigrants under the law.

In a hastily scheduled hearing, he said he did not believe the law offered grounds for the president’s action, and he ordered any flights that had departed with Venezuelan immigrants under the executive order to return to the United States “however that’s accomplished — whether turning around the plane or not.”

“This is something you need to make sure is complied with immediately,” he directed the government.

Lee Gelernt, a lawyer for the American Civil Liberties Union, which sued over the executive order, said in an interview after the hearing that he believed two flights were “in the air” on Saturday evening.

During the hearing, Judge Boasberg said he was ordering the government to turn flights around given “information, unrebutted by the government, that flights are actively departing.”