An inspector general within the Treasury Department is investigating the Trump administration's handling of a congressional request for President Trump's tax returns.

House Democrats are fighting for access to six years of Trump's financial records, which Treasury Secretary Stephen Mnuchin refuses to hand over, and filed a lawsuit in federal court demanding their disclosure.

Within that lawsuit, Democrats flagged a whistleblower complaint filed over the summer by a career Internal Revenue Service official alleging Treasury Department political appointees attempted to interfere in the audit process by pressing the IRS to ignore a requirement to scrutinize Trump's tax returns.

Richard Delmar, the acting Treasury inspector general, opened a review in response to a request by House Ways and Means Committee Chairman Richard Neal.

“Chairman Neal has asked Treasury OIG to inquire into the process by which the Department received, evaluated, and responded to the Committee’s request for federal tax information,” Delmar said in a statement to the Washington Post. “We are undertaking that inquiry.”

Neal, a Massachusetts Democrat, wrote the watchdog a letter this week that said, "I want to be assured that Treasury, including the [IRS], is enforcing the law in a fair and impartial manner and no one is endeavoring to intimidate or impede government officials and employees carrying out their duties."

Trump, along with Vice President Mike Pence, has refused to make public any of his recent tax returns, often claiming it is because they are under audit. Mnuchin, who has received consultation of the Justice Department, has resisted Democratic efforts to obtain Trump's tax returns, arguing their request lacked a “legitimate legislative purpose" and may be designed to do political damage to the president.

Another whistleblower complaint from an intelligence official, focused in part on a phone call between Trump and Ukraine's president, spurred House Speaker Nancy Pelosi to announce a formal impeachment inquiry last month.