The US Court of Appeals for the District of Columbia Circuit heard oral arguments in a lawsuit Trump filed arguing his accounting firm, Mazars LLP, does not need to comply with a House of Representatives Oversight Committee subpoena.

The three judges on the panel did not say how or when they would rule. But they repeatedly sparred with Trump's personal lawyer William Consovoy over his central argument that the subpoena is unconstitutional because it is "law enforcement" that would not further Congress' main task of enacting laws.

Judge David Tatel said the House is already working on legislation relating to presidential conflicts of interest and government ethics, and suggested that the financial records requested from Mazars are reasonably related to that effort.

"These bills have passed the House and are directly related to the subject of this subpoena," Tatel said.

The House Oversight Committee has also said it needs Trump's financial records to examine whether he broke the law by not disentangling himself from his business holdings, as previous presidents have done.

But Consovoy urged the judges to look at the "totality of the evidence," including media reports that House Speaker Nancy Pelosi told fellow Democrats that she wants to see Trump in prison.

Consovoy said Pelosi's remark makes clear that Congress' real objective with the Mazars subpoena is to investigate Trump so it can make him look bad and score political points.

"The court does not have to be naive ... and deny what is staring the court in its face," Consovoy said.

Judge Patricia Millett told Consovoy she was wary of second-guessing Congress' motives. If she adopted his argument, she would be essentially calling the House's proposed ethics laws "a ruse" for getting Trump's financial records, she said.

"Can we do that?" Millett asked, noting that courts have long been reluctant to block congressional subpoenas.

Mazars has avoided taking sides in the dispute and said it will "comply with all legal obligations."

In August an appeals court in New York will hear oral arguments in a challenge Trump brought seeking to block similar congressional subpoenas issued to Deutsche Bank AG and Capital One Financial Corp.

Trump is refusing to cooperate with a series of investigations on issues ranging from his tax returns and policy decisions to his Washington hotel and his children's security clearances.