WASHINGTON (Reuters) - U.S. Treasury Secretary Steven Mnuchin defied a congressional subpoena seeking six years of President Donald Trump’s tax returns on Friday, all but guaranteeing a federal court battle with Congress over the records.

In a widely expected move, Mnuchin rejected a demand for the documents from House Ways and Means Committee Chairman Richard Neal, saying the panel lacks “a legitimate legislative purpose” for obtaining the tax records that Democrats view as critical to their efforts to investigate Trump and his presidency.

“We are unable to provide the requested information in response to the committee’s subpoena,” Mnuchin said in a letter to Neal, released ahead of a 5 p.m. EDT (2100 GMT) deadline for delivering the documents.

Neal later issued a statement, saying he was “consulting with counsel on how best to enforce the subpoenas moving forward.”

Hours earlier, the Democratic chairman had said he was inclined to turn to federal court to obtain Trump’s tax returns, if the administration missed the deadline. “We will likely proceed to court as quickly as next week,” Neal had told reporters.

Asked whether he would also pursue contempt charges against administration officials, Neal told reporters: “I don’t see that right now as an option. I think that the better option for us is to proceed with a court case.”

Trump’s refusal to cooperate in numerous congressional probes of him, his family and his presidency is forcing Democrats, who control the House of Representatives, to look to the courts to enforce their oversight powers under the U.S. Constitution.

The likely decision to avoid contempt proceedings disappointed some Democrats on Neal’s tax panel.

“This is a way for some congressmen to go south on the issue: leave it to the courts. It really absents us from our responsibilities,” said Representative Bill Pascrell, who helped lead the push to obtain Trump’s tax returns.

OTHER DEMOCRATS MOVE TOWARD CONTEMPT

Unlike Neal, other top Democrats faced with administration defiance over inquiries have moved toward contempt charges.

House Judiciary Committee Chairman Jerrold Nadler’s panel voted last week to recommend that the House cite Attorney General William Barr with contempt of Congress for defying a subpoena for U.S. Special Counsel Robert Mueller’s unredacted Russia investigation report.

Trump’s decision to assert executive privilege over Mueller-related material last week has stymied efforts by Democrats to get current and former members of the executive branch to testify, including Mueller himself, according to congressional aides.

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Democrats had sought to have Mueller testify by May 23, but sources familiar with the matter said on Friday that Mueller was unlikely to appear before the committee.

Democrats could move forward with more contempt citations as early as next week. Nadler has threatened to hold former White House counsel Don McGahn in contempt, if he fails to show up for a hearing slated for Tuesday.

House Intelligence Committee Chairman Adam Schiff is also planning “enforcement action” against the Justice Department over a separate Mueller-related subpoena.

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Democratic leaders are considering bundling separate contempt citations into a single House of Representatives package to bring to a floor vote later this year.

On Wednesday, White House counsel Pat Cipollone sent a letter to Nadler, saying Congress has no right to conduct a “do-over” of Mueller’s Russia probe, and that it would not participate in his committee’s investigation.

But congressional pressure on Trump is only expected to intensify.

Schiff’s committee meets on Monday to release closed-door testimony by former Trump lawyer Michael Cohen, who is in prison. Cohen talked to the panel in March about issues including Trump’s involvement in pursuing a Moscow tower project during the 2016 presidential election. Trump at the time publicly denied any links to Russia.

On Thursday, House Oversight Committee Chairman Elijah Cummings announced another probe into the Trump administration, targeting what Cummings called “secret ethics waivers” allowing political appointees to continue working on matters they worked on before entering government.

In a statement, Cummings said he had requested that the administration turn over copies of waivers for political appointees to let them conduct official business, despite potential conflicts of interest.