(CNN) The Justice Department released Friday a new legal opinion supporting the Treasury secretary's refusal to hand over President Donald Trump's tax returns.

"The law required Treasury to deny that request," Assistant Attorney General Steven Engel wrote in a strongly-worded 33-page opinion, concluding that the demand for tax information amounted to an "unprecedented" use of the House Ways and Means Committee's authority and raised a "serious risk of abuse."

Committee Chairman Richard Neal has been in a pitched battle with the administration for weeks, finally issuing a subpoena to Treasury and the IRS in May after the agencies rebuffed the Democrat's request for six years of the President's personal and business tax returns.

Neal has invoked a little-known provision of the tax code that states the Treasury secretary "shall furnish" the committee with the return information, and he has claimed that returns are needed to consider legislative proposals related to federal tax laws and the IRS's practice of auditing sitting presidents.

The Office of Legal Counsel at the Justice Department acknowledged Neal's authority and that the plain text of the tax code does not require the committee to provide any purpose in support of its request for tax information. However -- pointing to a number of public statements from Neal and attempts from other Democrats to force the release of the tax returns -- OLC concluded that Neal's proffered oversight justification was merely "pretextual," and the "real reason" for requesting the returns was to make them public.

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