WASHINGTON - Treasury Secretary Steven Mnuchin on Friday rejected a subpoena from House Democrats demanding copies of President Donald Trump's tax returns, setting the stage for a court battle over the documents.

Mnuchin said the House Ways and Means Committee's request "lacks a legitimate legislative purpose," citing the legal advice of the Department of Justice, and said he was not authorized to hand over the returns.

Last week, Committee Chairman Richard Neal, D-Mass., issued subpoenas that gave Mnuchin and Internal Revenue Service Commissioner Charles Rettig until Friday at 5 p.m. to turn over Trump's financial records.

The denial sets up a federal court fight over Trump's financial records, the source of significant speculation since Trump refused to release them during the 2016 presidential campaign in a break with decades of precedent. Legal experts say Neal is likely to sue the administration in federal court to enforce the subpoenas.

"A lawsuit is the next step. There's no negotiation here," said Steve Rosenthal, an expert at the Tax Policy Center, a non-partisan think-tank.

The expected court battle is part of the broader clash between House Democrats and the White House over a range of oversight issues.

House Intelligence Committee Chairman Adam Schiff, D-Calif., said earlier this week he will hold meetings to discuss holding Trump Attorney General William Barr in contempt for ignoring the committee's subpoena of an unredacted copy of the special counsel's report on Russian interference in the 2016 presidential election. Rep. Jerrold Nadler, D-N.Y., chair of the judiciary committee, has also moved to hold Barr in contempt for defying an additional subpoena for the report and other documents.

Neal could respond by going to a congressional body to authorize a lawsuit in federal court against the two Trump administration officials. That body, the Bipartisan Legal Advisory Group, is controlled by Democrats.

Legal experts have said Mnuchin's refusal to turn over the returns is unprecedented, noting a 1924 law that explicitly gives lawmakers the authority to seek the records. Mnuchin and congressional Republicans have cited concerns over taxpayer privacy in denying the request, accusing Democrats of seeking to "weaponize" the IRS.

Rep. Bill Pascrell, D-N.J., a member of the House Ways and Means Committee, suggested in an interview that Mnuchin may be subject to a fine, a contempt vote, or even possibly jail time for ignoring what he said was the clear intent of the law.

"I would throw the book at these guys," Pascrell said. "We don't have a kingdom, regardless of the imagination of some public officials ... you deserve the full weight of the law. Let's not play games anymore."

Neal outlined a similar case in his subpoena, arguing: "The IRS is under a mandatory obligation to provide the information requested."

- - -

The Washington Post's JM Rieger contributed reporting to this story