A draft IRS legal memo obtained by The Washington Post says the Treasury Department must turn over tax returns to Congress unless the president asserts executive privilege over them.

That confidential memo contradicts the Trump administration's rationale for so far refusing to provide Congress with President Donald Trump's tax information, defying repeated requests by the House Ways and Means Committee.

Treasury Secretary Steven Mnuchin has said the returns are not required because there is no legislative purpose being pursued by Congress. But the memo says such disclosure is "mandatory, requiring the Secretary to disclose returns, and return information, requested by the tax-writing Chairs," the Post reported.

Federal law gives congressional tax committees the right to obtain and review the otherwise confidential federal tax information of any taxpayer. The IRS memo says the law “does not allow the Secretary to exercise discretion in disclosing the information provided the statutory conditions are met,” rejecting Mnuchin's rationale.

Mnuchin's "obligation to disclose return and return information would not be affected by the failure of a tax writing committee . . . to state a reason for the request,” the memo states, adding that the “only basis the agency’s refusal to comply with a committee’s subpoena would be the invocation of the doctrine of executive privilege."

The IRS told the Post that the memo, which is unsigned and doesn't refer to Trump, was a draft document written by an internal lawyer and does not represent the agency's official position.

The report comes after the Treasury Department said last week that it would not comply with congressional subpoenas to provide six years of Trump’s tax returns to the House Ways and Means Committee — making it increasingly likely Democrats will have to take the battle to court.

Mnuchin said Wednesday in testimony at a House Financial Services Committee hearing that he has "had no conversations with the president or anyone in the White House about delivering the president's tax returns to Congress."

Trump has refused to make his tax returns public, becoming the first president in four decades to do so. Trump has cited ongoing audits as preventing him from releasing them, although such review would not preclude him from releasing the information.