A federal appeals court weighed on Tuesday whether to allow U.S. District Judge James Boasberg to move forward with a criminal contempt inquiry into Trump administration officials over last year’s deportations of Venezuelans to El Salvador, as Justice Department lawyers allege the judge’s investigation is “unlawful.”

Boasberg, an appointee of former President Barack Obama, has been a thorn in the Trump administration’s side by issuing multiple adverse rulings against the president. He previously found probable cause to hold government officials in contempt for allegedly violating an order to halt the deportation of a group of Venezuelans being flown to a maximum security prison in El Salvador. The federal judge had sought to determine which officials had allegedly violated his order, even examining then-Homeland Security Secretary Kristi Noem, through additional fact-finding but was shut down by a three-judge panel on the U.S. Court of Appeals for the D.C. Circuit earlier this year. The full bench of the D.C. Circuit elected to review the case, setting up Tuesday’s lengthy arguments over whether to allow Boasberg’s inquiry to move forward.