A U.S. judge on Monday ordered Trump administration officials to explain whether the administration violated his order when they deported hundreds of Venezuelan gang members over the weekend and potentially set up a constitutional clash between the president and the federal judiciary.

The Trump administration has transferred hundreds of immigrants to El Salvador even as a federal judge issued an order temporarily barring the deportations under an 18th century wartime declaration targeting Venezuelan gang members, officials said Sunday. Flights were in the air at the time of the ruling.

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