Michigan Democrat Rep. Rashida Tlaib told Treasury Secretary Steven Mnuchin at a testy hearing on Wednesday that he should seek "personal" legal advice, effectively issuing a thinly veiled threat following his refusal to turn President Trump's personal tax information over to Congress.

"I would be remiss, as somebody that truly believes in the rule of law, as somebody that has practiced law and is an attorney, I would advise you, secretary, to get personal legal advice," Tlaib said, smirking slightly. "The cover-up by this administration, it goes beyond just providing the taxes.

"You can consult the Department of Justice but you, personally, making decisions – not on the best part of the American people, but to cover up the occupant of the White House – I think you need to be very, very clear about what your role is and what your responsibility is to the American people," she continued.

Tlaib added: "So, secretary, please seek out legal advice, personally, of what your obligations are, because the Department of Justice is not protecting you, it's protecting the president."

House Speaker Nancy Pelosi echoed Tlaib's remarks, charging later Wednesday that the president was "engaged in a cover-up." Responding to Pelosi's claim in a fiery Rose Garden press conference, Trump said simply, "I don't do cover-ups," and called for an end to "phony investigations."

Trump added that he had walked out of a meeting with Pelosi and Senate Majority Leader Chuck Schumer, D-N.Y., and he asserted that pursuing infrastructure legislation would be impossible while he was still under aggressive investigation.

Mnuchin, for his part, testified he has no idea who wrote a confidential Internal Revenue Service legal memo that says that tax returns must be given to Congress unless the president asserts executive privilege.

DEM WANTS TRUMP OFFICIALS JAILED FOR NOT TURNING OVER TAX RETURNS

Appearing before the House Financial Services Committee, Mnuchin said he was not aware of the existence of the memo until reporters from The Washington Post asked about it.

Mnuchin said it was a draft document. He told the committee he believed he was following the law by refusing to turn over six years of Trump's tax returns, which have been requested by Ways and Means Committee Chairman Richard Neal, D-Mass.

Mnuchin said he expected the dispute to ultimately be decided by the courts.

Mnuchin has refused to turn over the tax returns despite a 1924 law that gives the chairs of the tax-writing committees in Congress the power to request the returns of any taxpayer.

Mnuchin last Friday refused to obey a congressional subpoena to turn over the returns, saying the request "lacks a legitimate legislative purpose."

Mnuchin told lawmakers that he had not had any discussions on the issue with Trump, who has said repeatedly that he can't turn over his taxes because he is under IRS audit. Trump has not asserted executive privilege to protect the returns.

WHAT DID CONFIDENTIAL DRAFT IRS MEMO ON TRUMP TAX RETURNS SAY?

Neal has said he expects to bring a lawsuit to force the administration to comply with his subpoena.

When a number of Democrats pressed Mnuchin on the 1924 law, Mnuchin said that "weaponizing the IRS is a major concern of ours which affects taxpayers of both parties."

"So, Secretary, please seek out legal advice, personally, of what your obligations are." — Michigan Democrat Rep. Rashida Tlaib

Mnuchin's appearance Wednesday before the House Financial Services Committee was a continuation of a hearing that had ended with a tense standoff earlier in the month. Back then, Mnuchin complained to Committee Chairwoman Maxine Waters, D-Calif., that the hearing was going on too long and forcing him to miss a meeting with the head of a foreign country.

Waters and Mnuchin were cordial with each other during Wednesday's hearing. Mnuchin stayed until all lawmakers on the panel had the chance to ask their questions, which covered a number of issues -- from Trump's taxes to the status of the redesign of the $20 bill and the trade dispute with China.

The administration increased tariffs on an initial $200 billion of Chinese goods last week from 10 percent to 25 percent. But broadening the tariffs to another $300 billion in goods will not go into effect until after public hearings and a final decision by the administration.

Fox News' Alex Pappas and The Associated Press contributed to this report.