US President Donald Trump has sued his own accounting firm and the Democratic chairman of the House Oversight Committee at the same time in a bid to block the committee from obtaining his financial records through a subpoena.

The lawsuit, filed on Monday in a federal court in the District of Columbia, seeks a court order to quash a subpoena issued last week by the committee. Trump’s lawyers also are asking a federal judge to temporarily block the subpoena until the court has had a chance to review their request, The Washington Post.

“There is no possible legislation at the end of this tunnel,” Trump’s attorneys wrote in their brief, talking about the Oversight Committee’s inquiry into whether the President misled his lenders by inflating his net worth.

“The Oversight Committee is instead of assuming the powers of the Department of Justice, investigating (dubious and partisan) allegations of illegal conduct by private individuals.”

Trump’s private attorney, Jay Sekulow, issued a statement saying: “We will not allow Congressional Presidential harassment to go unanswered.”

The suit came as House Democrats issued another subpoena.

The chairman of the House Judiciary Committee on Monday ordered former White House counsel Donald McGahn to testify before the panel next month and hand over documents and records pertaining to federal investigations of Trump, his finances, his campaign and allegations he sought to obstruct justice.

He is the first former White House employee to receive a subpoena for congressional testimony in the wake of Special Counsel Robert Mueller redacted report on the Russian interference being released to the public.

The Trump Organization, the President’s private business, also is listed as a plaintiff in the lawsuit.

Trump still owns the business, although he says he has given up day-to-day control to his sons Eric Trump and Donald Trump Jr.

Trump Organization attorney Alan Garten told The Washington Post that the subpoena was an “unprecedented overreach by Congress”.