WASHINGTON (CN) — A whistleblower in the Trump administration stepped forward over two months ago to warn House Democrats that the Treasury Department is mishandling the president’s long-shrouded tax returns.

The House Ways and Means Committee included the explosive detail among dozens of exhibits to a lawsuit it brought in July, informing Treasury Secretary Steve Mnuchin that an unsolicited communication the committee received from a federal employee included “credible allegations” of possible misconduct including “inappropriate efforts to influence” the mandatory auditing of presidential income tax returns.

“This is a grave charge that appreciably heightens the Committee’s concerns about the absence of appropriate safeguards as part of the mandatory audit program and whether statutory codification of such program or other remedial, legislative measures are warranted,” Committee Chairman Richard Neal told Mnuchin in the Aug. 8 letter.

The letter goes on to remind Mnuchin that the committee has repeatedly raised concerns now matched by the whistleblower that IRS employees may be subject to “undue influence” when conducting mandatory audits of President Donald Trump’s tax returns.

The government had responded to these previous claims, calling them “unfounded.”

But the letter from Neal says the whistleblower report undercuts the department’s denial of wrongdoing.

“The allegations received by the committee cast doubt on this statement and underscore the pressing need for complete and meaningful oversight of the mandatory audit program,” Neal wrote in the letter.

Labeled Exhibit QQ, the Neal letter is part of a lawsuit that accuses the Treasury Department of shielding the president from congressional oversight by withholding his tax returns.

“Without reviewing the requested return materials, the committee cannot ensure that the IRS’s audit process is functioning fairly and effectively, understand how provisions of the tax code are implicated by President Trump’s returns, or exercise its legislative judgment to determine whether changes to the code may be warranted,” the complaint states.

The committee moved for summary judgment in August. It has not responded to a request for comment.

While the tax case includes no detail about the identity of the whistleblower, there is no connection to the unknown individual who brought a complaint this summer about President Donald Trump ostensibly soliciting a foreign power’s interference in the 2020 election.