WASHINGTON (AP) — A federal judge ruled Monday that the Trump administration must give legal due process to Venezuelan migrants flown to a notorious prison in El Salvador, either by providing court hearings or returning them to the U.S.

U.S. District Judge James Boasberg ordered the government to come up with a plan within two weeks for the men, who have since been returned to Venezuela in a prisoner swap.

“Plaintiffs should not have been removed in the manner that they were, with virtually no notice and no opportunity to contest the bases of their removal, in clear contravention of their due-process rights,” Boasberg wrote.

It’s the latest development in a case that’s been a legal flashpoint in the administration’s sweeping crackdown on immigration. It started in March, after Trump invoked an 18th century wartime law to send Venezuelan migrants accused of being gang members to a mega-prison known as the Terrorism Confinement Center, or CECOT.

Two planeloads of men were flown to the prison, despite a verbal order from Boasberg for the aircraft to turn around. Boasberg subsequently started a contempt investigation, though the dramatic battle between the judicial and executive branches has been paused by an appeals court.

The administration has denied violating his order. The White House did not have immediate comment on Monday’s ruling.

More than 200 migrants were released back to Venezuela in a prisoner swap with the U.S. in July.

The ruling from Boasberg, who was appointed to the federal bench by Democratic President Barack Obama, opens a path for them to challenge the allegation that they’re members of the Tren de Aragua gang and subject to removal under the Alien Enemies Act.

“This critical ruling makes clear that the Trump administration cannot simply spirit people off to a notorious foreign prison with zero due process and simply walk away. There are consequences,” said ACLU attorney Lee Gelernt, who represents the migrants.