'...The House effectively delegates its oversight responsibilities to its committees which
can issue subpoenas for documents or testimony from the executive branch. In the matter of tax returns, the law could not be more clear (see
Code sec. 6103(f)): Upon written request by either the Chairman of either the House Ways and Means Committee or the Senate Finance Committee, the Treasury Secretary “
shall furnish such committee with any return or return information specified in such request.” The Ways and Means Committee may share these tax returns and related information with the full House, assuming there is a
legitimate purpose for doing so.
Congress gave itself the right to review any return or return information in 1924,
in the aftermath of two controversies. One was the Teapot Dome scandal, where senior officials in the Harding Administration granted public oil field leases in exchange for bribes. The other involved allegations that Treasury Secretary Andrew Mellon continued to own many business interests while serving in government.
Some believed the Bureau of Internal Revenue, the precursor to the IRS, showed favoritism to the secretary and his businesses.
[...]
Congress Can And Should Demand President Trump's Tax Returns