"If Secretary Mnuchin fails to comply with this deadline, Chairman Neal has no choice but to subpoena the Treasury Department and force the IRS to comply with this request," Tax March spokesman Ryan Thomas said Tuesday. "If Secretary Mnuchin or other Trump administration officials continue to stymie the process, House Democrats should look into holding them in contempt of Congress."
Failure to comply with a subpoena also could lead to Mnuchin being held in contempt of Congress, along with a court order of daily fines or even jail until he does comply, experts say.
"To me the person who's most vulnerable to this is Mnuchin because, of course, the statute directs Mnuchin to do something, so if he doesn't comply then he's the one in violation," said George K. Yin, a professor at the University of Virginia School of Law and former chief of staff of the Joint Committee on Taxation.
"Mnuchin could well be on the line here if (Democrats) seek to enforce" the request for Trump's tax returns, said William Alden McDaniel Jr., an attorney with Ballard Spahr LLP who has represented officials in both Republican and Democratic administrations targeted in congressional investigations.
Trump would be the first president since Richard M. Nixon not to release his tax returns, if Mnuchin ultimately doesn't comply with Neal's demand.
Trump has repeatedly said he would disclose them publicly once he was no longer under audit by the IRS. But presidents and vice presidents are automatically audited each year by law, and Rettig recently told a congressional committee there is no law barring the president from voluntarily making his returns public.
Neal first requested the tax returns in an April 3 letter to Rettig, giving him a week to comply. Though the statute Neal cited directs the Treasury secretary to furnish any requested returns to certain congressional committees, including Ways and Means, the law also enables the Treasury secretary to delegate such authority, which occurred in 1982.
If Treasury wants such authority back, Democrats argue the statute says the secretary must provide 30 days' notice to lawmakers. Nonetheless, Rettig has deferred to Mnuchin in this instance.
When April 10 arrived, Mnuchin responded he wouldn't be able to meet the deadline and that he'd consult with the Justice Department on whether to comply. He wrote Neal's request "raises serious issues concerning the constitutional scope of Congressional investigative authority."
Neal's authority to seek the president's tax returns stems from Section 6103 of the tax code, which states that upon "written request" from the chairman of either of the two tax-writing committees "the Secretary shall furnish such committee with any return or return information specified" in the request.