The House Ways and Means Committee filed a lawsuit on Tuesday to enforce subpoenas and obtain President Donald Trump‘s tax returns as the legal battle over the president’s finances escalates.

The lawsuit was filed in D.C. court against the Secretary of the Treasury Department Steve Mnuchin and the head of the IRS Charles Rettig.

The Chairman of the Ways and Means Committee, Richard Neal, is using IRS provision 163, a rarely used clause that allows the chairman of the Ways and Means Committee and the Senate Finance Committee to obtain an individual’s tax records for a legitimate legislative purpose.

This is the most recent step in a long, drawn-out battle between the House and the Trump administration over the president’s financial records. Neal originally requested the documents on April 3 and was then denied by the Treasury Department in early May. Neal then subpoenaed the Treasury Department and the IRS on May 10 to force the agencies into handing over Trump’s tax returns.

“In refusing to comply with the statute, Defendants have mounted an extraordinary attack on the authority of Congress to obtain information needed to conduct oversight of Treasury, the IRS, and the tax laws on behalf of the American people who participate in the Nation’s voluntary tax system,” House attorneys wrote in the complaint.

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This is not the first House committee to sue the government in order to obtain the president’s financial records. The House Oversight Committee, the House Intelligence Committee, and the House Financial Services Committee have all gone through the same process as the Ways and Means Committee, with their initial requests and subpoenas denied.

The president has been ardently fighting back against the House investigations, labeling them as witch hunts and accusing the Democrats of presidential harassment. His passionate opposition to the release of his tax returns, documents that many Democratic 2020 candidates willing divulged, raises the question of what he has to hide.