House Ways and Means Chairman Richard Neal is filing a lawsuit against the U.S. Treasury Department in an effort to compel the IRS to turn over President Trump's tax returns.

Why it matters: Treasury Secretary Steven Mnuchin has denied multiple requests for Trump's tax returns, including a subpoena from the House Ways and Means Committee in May — arguing that the demands "lack a legitimate legislative purpose." The result of Mnuchin's defiance is likely to be a protracted court battle.

What they're saying:

The lawsuit argues that a section of the IRS code requires "in mandatory terms that Treasury 'shall furnish'" the House Ways and Means Committee with "any" tax return information that is requested, and that Trump has denied the request for what the committee believes is the first time ever.

In response to Treasury's argument that the request lacks a "legitimate legislative purpose," the lawsuit claims that nothing in the relevant IRS code requires an explanation. Even if a reason were required, the lawsuit argues that the committee needs the materials for its investigation into tax laws and policies related to presidential tax returns and tax law compliance by Trump.

It also argues that "the committee's power to conduct oversight and investigations is firmly rooted in Congress’s Article I legislative authority."

The other side: In a legal opinion released last month, the Justice Department previewed what is likely to be the Trump administration's argument against releasing the tax returns. Read it here.

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