One House committee chairman officially fired off a request Wednesday for six years of President Trump’s tax returns, as another won the authority to issue subpoenas to demand special counsel Robert Mueller’s full investigative file of Mr. Trump.

The twin moves marked escalations in Democrats’ scrutiny of the president, and both threatened to spark legal battles.

House Ways and Means Chairman Richard E. Neal, Massachusetts Democrat, sent his demand to the IRS for the president’s tax returns from 2013 through 2018. He also asked for returns from eight Trump entities, including his revocable trust and his golf course in Bedminster, New Jersey.

SEE ALSO: Democrats officially demand IRS turn over Trump tax returns

Mr. Neal said his committee is thinking about passing legislation on government audits of presidents and therefore has the right under its oversight powers to demand to see the information.

He set an April 10 deadline for the IRS to comply.

Mr. Trump, saying he is under audit, has repeatedly rebuffed calls to make his tax returns public. He signaled Wednesday that he is likely to battle Mr. Neal’s demand.

SEE ALSO: Dems approve subpoena for Mueller report, investigative files

“Until such time as I’m not under audit, I would not be inclined to do it,” he told reporters at the White House.

Meanwhile, the House Judiciary Committee voted along party lines to give Chairman Jerrold Nadler, New York Democrat, the power to issue a subpoena to demand that the Justice Department turn over the special counsel’s report into Mr. Trump and Russian interference in the 2016 election, as well as all investigative files that Mr. Mueller developed.

That expansive subpoena was joined by other subpoenas for five former Trump White House officials, including onetime chief of staff Reince Priebus, former top attorney Donald McGahn and former chief strategist Steve Bannon.

The 24-17 committee vote did not issue the subpoenas, but it gave permission to send them at any time to Mr. Nadler, who would oversee any impeachment proceedings against Mr. Trump.

The subpoena would demand access to classified documents and to information that stemmed from the grand jury that Mr. Mueller relied upon during his investigation.

Under the law, grand jury proceedings are supposed to be sealed, though a court can unseal them.

“We need these materials to fulfill our constitutional obligation,” said Mr. Nadler, adding that Congress received classified data and grand jury information during impeachment-style investigations into President Nixon in the 1970s and President Clinton in the 1990s.

Republicans said the demand was premature.

Attorney General William P. Barr said he is planning to release as much of Mr. Mueller’s final report as possible this month.

The materials he isn’t releasing are supposed to be kept secret under the law, they said, and if Mr. Nadler wants to see those, he will have to go through a long legal battle in the courts asking them to unseal grand jury information.

Rep. F. James Sensenbrenner Jr. of Wisconsin, one of the Republican impeachment managers against Mr. Clinton in the 1990s, said he would join Mr. Nadler in making that request to the courts but added that approving the subpoena now would make no sense.

“Go to court and let the judge make the decision,” he said.

Mr. Nadler, though, said he wanted to have the subpoena in hand first and then go to court if necessary.

Mr. Nadler was on the other side of the debate in the 1990s, arguing that the Clinton investigation information should not be provided to Congress. He lost then and now says that precedent holds today for the Mueller investigation into Mr. Trump.

“Our chief constitutional obligation is to hold the president accountable, especially in an instance where the Department of Justice says it cannot hold the president accountable,” he said. “Those judgments must be made by Congress, not by a political appointee, the attorney general.”

If Mr. Nadler’s subpoena powers are challenged in court, then they are likely to be joined by Mr. Neal’s request.

Although Mr. Trump joked about the request for six years of returns — “is that all?” he said to reporters — the power to demand a taxpayer’s information is due to be tested.

The power rests in Section 6103 of the tax code, which orders that tax returns be kept private under federal law but includes a provision giving the heads of the tax-writing House Ways and Means and Senate Finance committees the ability to request “any return or return information.”

Although information that can be traced back to an individual is supposed to be viewed only in closed session by the committee, the expectation on Capitol Hill is that the information will quickly find its way into the public sphere, possibly through a vote by the full Ways and Means Committee.

Mr. Neal said Mr. Trump’s information is needed to write better laws, but fellow Democrats made clear that they plan to expose the president politically.

“For much of his adult life, Trump has used his power to shield himself from scrutiny or accountability. Subjecting his tax records to sunlight can finally hold him to both,” said Rep. Bill Pascrell Jr., New Jersey Democrat.

Rep. Kevin Brady of Texas, the top Republican on Mr. Neal’s committee, urged the Treasury Department and the IRS to refuse the request.

“This particular request is an abuse of the tax-writing committees’ statutory authority, and violates the intent and safeguards of Section 6103 of the Internal Revenue Code as Congress intended,” he said in a letter to Treasury Secretary Steven T. Mnuchin.

Sen. Ron Wyden of Oregon, the top Democrat on the Senate Finance Committee, said he doubts Mr. Mnuchin will be able to resist complying with Mr. Neal’s request.

“The law is crystal clear,” he said. “I expect the Treasury Department to comply in a timely manner.”

He said he wants the Republican chairman of the Finance Committee, Sen. Chuck Grassley of Iowa, to make the same request for the Senate.

Mr. Grassley has criticized requests for Mr. Trump’s tax returns as an effort to “weaponize” the tax law for political purposes. But he also has said that if the House did it, then he would make the same request to prevent any mischief on Democrats’ part.

On Wednesday, a representative for Mr. Grassley said he takes a dim view of Mr. Neal’s move.

“Those seeking an individual’s personal tax returns to exact political damage would be opening the door to future abuses of power and would poison the public trust in the ability of the IRS to keep personal information private. That’s an outcome every taxpayer and their elected representatives should want to avoid.”