Congressional Democrats will "never" obtain US President Donald Trump's tax returns, acting White House chief of staff Mick Mulvaney said on Sunday.

"Nor should they (obtain the documents)" Mulvaney told "Fox News Sunday." "Keep in mind, that's an issue that was already litigated during the election. Voters knew the President could have given over his tax returns, they knew that he didn't and they elected him anyway. Which, of course, is what drives the Democrats crazy."

Mulvaney's comments come several days after House Ways and Means Committee Chairman Richard Neal, a Democrat from Massachusetts, formally requested six years of Trump's personal tax returns from the Internal Revenue Service, CNN reported.

In a letter sent on Wednesday to the IRS, Neal cites a little known IRS code in his request for six years of Trump's personal tax returns from 2013 to 2018. He also requested the tax returns of eight of Trump's business entities, a nod to escalating pressure from liberals in the caucus who have argued that Trump's personal returns wouldn't sufficiently paint a picture of the President's financial history.

"The Democrats are demanding that the IRS turn over the documents and that is not going to happen and they know it," Mulvaney told Hemmer, adding that the request "is a political stunt."

Trump's outside counsel, William Consovoy of the law firm Consovoy McCarthy Park PLLC, argued in a statement Friday that the requests for Trump's tax information "are not consistent with governing law, do not advance any proper legislative purpose, and threaten to interfere with the ordinary conduct of audits."

House Intelligence Committee Chairman Adam Schiff cast doubt Sunday on the ability of Trump's legal team to withhold his taxes, saying, "there is no legal ground for them here."

"The statute says the IRS shall provide these returns to the Congress upon request. When the Republicans asked similarly for returns when they were running that committee, including the returns of the Obama for America organization, (the chairman) gave no explanation for why he sought those returns or how many returns he was seeking or what organisations," he told CNN on "State of the Union."

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"He just asked, and the IRS says you can have them because we shall provide them. And I think that's how it's going to end up here, too."

The President has said previously that he would release his taxes but for an audit he has claimed to be under for years. (IANS)