Judge Amit Mehta, a US district judge, heard oral arguments on whether Mazars must comply with the subpoena issued by the House of Representatives Oversight Committee.
The hearing marks the first time that a federal court has engaged with the ongoing probe by Democrat lawmakers into Trump’s business affairs.
Trump has sued to block Mazars from supplying financial records to Congress, in a direct attempt to counter the committee’s subpoena.
In the hearing on congressional subpoenas, judge Mehta asked, “Am I right, there isn’t a single Supreme Court case or appellate case since 1880 that has found a congressional subpoena overstepped its bounds?
“I agree there are outer limits, but it’s not clear to me what they are,” he added.
The judge’s comments cast doubt on the idea that the courts could limit Congress’ ability to investigate the president.
Trump’s attorney, William Consovoy, argued throughout the hearing that the Congress investigation attempt is unconstitutional.
Judge Mehta disputed that claim, however, saying that he believes Congress has an “informing function” that doesn’t require an explicit legislative purpose to justify itself when investigating the president.
He has said that he will issue a ruling in writing by next week.