A federal judge on Tuesday ordered the administration of Donald Trump to not let a group of migrants being flown to South Sudan leave the custody of U.S. immigration authorities after saying they appeared to have been deported in violation of a court order.

U.S. District Judge Brian Murphy in Boston, during a hastily arranged virtual hearing, said that while he was not going to order the airplane to turn around, that was an option the U.S. Department of Homeland Security could employ to comply with his order.

Murphy warned that officials could be held in criminal contempt if he found they violated his previous order barring the swift deportation of migrants to countries other than their own before they could raise any concerns that they might face torture or persecution there.