Trump's treasury chief, who oversees the IRS, cited "complicated legal issues" and bemoaned "an arbitrary deadline" set by Congress, while saying he would answer in that time frame.
A new letter by Rep. Richard Neal, the House Ways and Means Committee chairman, comes after the Trump administration asked for more time to consider his initial request last week. Neal had requested six years of Trump's personal and business tax returns.
Neal, D-Mass., argues that a 1920-era law saying the IRS "shall furnish" any tax return requested by Congress "is unambiguous and raises no complicated legal issues" and that the Treasury Department's objections lack merit.
The letter to IRS Commissioner Charles Rettig is the latest exchange in a tug of war over Trump's returns, which would give lawmakers far greater insight into the president's business dealings and potential conflicts of interest as it exercises its oversight role.
Asked about the letter Saturday, Treasury Secretary Steven Mnuchin said he would respond to within the new deadline set by Neal but he did not promise to produce Trump's tax returns by that time. Mnuchin is the Cabinet secretary that oversees the IRS.
Mnuchin took issue with Neal's characterization of the dispute as a straightforward issue in light of the law governing the matter.
"These are complicated legal issues and I think it is more important to the American taxpayers that we get this right than we hit an arbitrary deadline," Mnuchin told reporters. "I would just emphasize this is a decision that has enormous precedence in terms of potentially weaponizing the IRS."
Mnuchin said that Treasury Department lawyers have been working "diligently" to research the issues involved and have been in contact with Justice Department attorneys. But he said he has not personally discussed the issue with Attorney General William Barr.
Mnuchin said he thought Neal was just picking arbitrary deadline and he refused to speculate how the administration would proceed if the issue goes to court.
Trump declined to provide his tax information as a candidate in 2016 and as president, something party nominees have traditionally done in the name of the transparency. By withholding his tax returns, Trump has not followed the standard followed by presidents since Richard Nixon started the practice in 1969.
Asked repeatedly at a House hearing Tuesday whether any regulation prohibited a taxpayer from disclosing returns when under audit, Rettig responded "no."
The issue appears sure to end up in federal court. With an eye to a legal challenge, Neal told Rettig that he has two weeks to respond — by 5 p.m. on April 23. If Rettig fails to do so, Neal said he will interpret as denying the request, which could pave the way for a court battle. Neal also could seek the returns through a subpoena.
Mnuchin had told Neal this past week that he needs more time to consider the unprecedented demand for Trump's returns and needs to consult with the Justice Department about it.
At congressional hearings, Mnuchin accused lawmakers of seeking Trump's returns for political reasons. But he also acknowledged his "statutory responsibilities" and that he respects congressional oversight. Some Treasury-watchers observe that Mnuchin's decision to consult with the Justice Department could suggest that Treasury lawyers believe Neal has a legal right to Trump's returns.
Neal said Saturday that the administration has no right "to question or second guess" his motivations.
William Consovoy, whose firm was retained by Trump to represent him on the matter, has written the Treasury's general counsel and said the congressional request "would set a dangerous precedent" if granted and that the IRS cannot legally divulge the information.
AP Economics Writer Martin Crutsinger contributed to this report.