In a letter to Rep. Richard Neal (D-MA), who chairs the House Ways and Means Committee, US Secretary of the Treasury Steve Mnuchin said he wouldn't approve the release of US President Donald Trump's tax returns because the committee's request for them "lacks a legitimate legislative purpose."

Mnuchin explained in the Monday letter that because "the committee's request is unprecedented," he sought the counsel of the Department of Justice on whether or not the committee's request was legitimate according to past US Supreme Court rulings on the committee's statutory authority.

The DOJ has not commented on the matter. However, Mnuchin's letter does say the department "intends to memorialize its advice in a published legal opinion as soon as possible."

Neal has sent three requests to Mnuchin for the information, on April 3 and a second demanding an answer no later than April 23. However, as that date came and went, the congressman grew increasingly critical of the Treasury and the Internal Revenue Service (IRS), which he believed were stalling for time.

"It is not the proper function of the IRS, Treasury or Justice to question or second guess the motivations of the committee or its reasonable determinations regarding its need for the requested tax returns and return information," Neal wrote to IRS Commissioner Charles Rettig on April 23. "Please know that if you fail to comply, your failure will be interpreted as a denial of my request."

House Democrats have sought Trump's tax returns in a renewed push to dig up dirt on the Republican president after it became apparent that Special Counsel Robert Mueller's report on alleged Russian collusion would not deliver them a way to be rid of the president. However, Democrats have long sought the real estate mogul's tax documents, as he is the first president to refuse their disclosure since President Richard M. Nixon.

Other congressional bodies have also sought financial information about the president in recent days, with Trump's lawyers suing last week to block nine banks from having to turn over the president's financial records to House Financial Services, House Intelligence and House Oversight Committees, which subpoenaed the documents.

"Whether it is refusing to sit down in an interview with Mueller or whether it is constantly obstructing justice by trying to stop testimonies and stop people from cooperating, whether it is filing a lawsuit, he obviously has something to hide," House Financial Services Committee Chairperson Maxine Waters (D-CA) said last week. "He's obviously afraid that we are going to learn more about his relationships with Deutsche Bank, more about his bank records, perhaps, more about whether or not there is money laundering that has been involved in some ways. We have enough information and we have enough to help us to guide us moving forward to help us with these subpoenas."

Mnuchin wrote Monday that "Although the Department [of Treasury] is unable to provide you with the requested confidential tax returns and return information, we renew our previous offer to provide information concerning the Committee's stated interest in how the IRS conducts mandatory examinations of presidents, as provided by the Internal Revenue Manual. If the Committee is interested, we remain committed to providing such an accommodation."

In response to Mnuchin's letter, Neal said in a statement Monday that he would "consult with counsel and determine the appropriate response."