In a letter to the IRS sent Wednesday and first obtained by CNN, Neal cites a little known IRS code in his request for six years of Trump’s personal tax returns from 2013 to 2018. He also requested the tax returns of eight of Trump’s business entities, a nod to escalating pressure from liberals in the caucus who have argued that Trump’s personal returns wouldn’t sufficiently paint a picture of the President’s financial history.

While the move will largely be seen by Republicans as a political escalation, Neal explained in the letter the request is part of his oversight role. Neal wrote that the committee needed Trump’s tax returns to consider legislation related to the IRS’s practice of auditing sitting presidents.

“Under the Internal Revenue Manual, individual income tax returns of a President are subject to mandatory examination, but this practice is IRS policy and not codified in the Federal tax laws,” Neal wrote in a letter to the IRS. “It is necessary for the committee to determine the scope of any such examination and whether it includes a review of underlying business activities required to be reported on the individual income tax return.”