Congressional Access to the President's Federal Tax Returns [Updated April 4, 2019] [open pdf - 636KB]
From the Document: "The Chair of the House Ways and Means Committee is reportedly preparing to send a request to the Treasury Department's Internal Revenue Service (IRS) to obtain President Trump's federal tax returns. This request appears prompted by the President's departure from the past practice of sitting presidents and presidential candidates voluntarily disclosing their recent tax returns. This Sidebar analyzes the ability of a congressional committee to obtain the President's tax returns under provisions of the Internal Revenue Code (IRC); whether the President or the Treasury Secretary might have a legal basis for denying a committee request for the returns; and, if a committee successfully acquires the returns, whether those returns legally could be disclosed to the public."
CRS Legal Sidebar, LSB10275
Congressional Research Service: https://crsreports.congress.gov/