A panel on the U.S. Court of Appeals for the 1st Circuit sharply questioned the Trump administration on Monday over its mandatory detention policy for undocumented immigrants, as the problem races toward the Supreme Court amid nationwide divisions in the judiciary.

The three-judge panel made up of U.S. Circuit Judges Lara Montecalvo, an appointee of former President Joe Biden; Sandra Lynch, an appointee of former President Bill Clinton; and Joshua Dunlap, an appointee of President Donald Trump, pressed Department of Justice lawyers over the administration’s stance that immigration law permits them to keep immigrants lacking permanent legal status detained pending removal proceedings. One of the major questions the judges asked dealt with whether an immigrant lacking permanent legal status already in the interior of the country is still legally “seeking admission,” a key term in the underlying law.