Lawyers for Donald Trump last month filed a lawsuit to block the committee's subpoena. (File)

A US judge on Monday ruled in favour of a US House of Representatives committee seeking President Donald Trump's financial records from his accounting firm, dealing an early setback to the Trump administration in its legal battle with Congress.

US District Judge Amit Mehta in Washington also denied a request by Trump to stay his decision pending an appeal.

Last Tuesday Mehta heard oral arguments on whether Mazars LLP must comply with a House of Representatives Oversight Committee subpoena.

Mehta said in Monday's ruling that the committee "has shown that it is not engaged in a pure fishing expedition for the President's financial records" and that the Mazars documents might assist Congress in passing laws and performing other core functions.

It was the first time a federal court had waded into the tussle about how far Congress can go in probing Trump and his business affairs.

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.

Trump's lawyers argued that Congress is on a quest to "turn up something that Democrats can use as a political tool against the president now and in the 2020 election."

Mehta's ruling will almost certainly be appealed to a higher court.

The House Oversight Committee claims sweeping investigative power and says it needs Trump's financial records to examine whether he has conflicts of interest or broke the law by not disentangling himself from his business holdings, as previous presidents did.

Lawyers for Trump and the Trump Organization, his company, last month filed a lawsuit to block the committee's subpoena, saying it exceeded Congress' constitutional limits.

Mehta was appointed in 2014 by Democratic former President Barack Obama, who was often investigated by Republicans in Congress during his two terms in office.

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