Neal originally demanded access to Trump's tax returns in early April under a law that said the IRS "shall furnish" the returns of any taxpayer to a handful of top lawmakers, including the chair of the tax-writing Ways and Means Committee.
The refusal to release 10 years of Trump's financial records tees up another likely legal fight between House Democrats and the Trump administration, which has stonewalled Democrats' ongoing congressional probes in recent weeks into Trump and his family's finances.
Consovoy wrote that Neal's request for the tax returns flouts "fundamental constitutional constraints", is driven by an intent to score political points, and would set a unsafe precedent if complied with.
Mnuchin said Monday he had made his decision in consultation with the US Department of Justice.
"In reliance on the advice of the Department of Justice, I have determined that the Committee's request lacks a legitimate legislative goal", Mnuchin wrote, "the Department is therefore not authorized to disclose the requested returns and return information".
A number of legal experts have said the law clearly states Mnuchin must release the president's tax returns upon request from Congress.
At the same time, he has not divested from his global business holdings, exposing him to accusations of potential conflicts of interest in conducting USA affairs. Time will tell, but I commend Mnuchin for not giving the Democrats any ammunition in their crusade to impeach Trump.
The Treasury Secretary went on to claim in the May letter that, contra assertions by House Democrats and legal scholars familiar with the underlying statute, that "the Department may not lawfully fulfill the Committee's request".
"We are under audit, despite what people said, and working that out", Trump told reporters at the White House. The likely options available to Democrats would be to subpoena the Internal Revenue Service for the returns or to file a lawsuit. "We can not allow this bad president to set bad precedent", said Rep. Lloyd Doggett (D-Texas). He concluded that the department was "not authorized to disclose the requested returns and return information".