WASHINGTON -- U.S. President Donald Trump directed his former White House Counsel Donald McGahn to defy a congressional subpoena Monday, citing a Justice Department legal opinion that maintains McGahn would have immunity from testifying about his work as a close Trump adviser. A lawyer for McGahn said he would follow the president's wishes and skip a House Judiciary Committee hearing on Tuesday.

Trump's action, the latest in his efforts to block every congressional probe into him and his administration, is certain to deepen the open conflict between Democrats and the president. Democrats have accused Trump and Attorney General William Barr of trying to stonewall and obstruct Congress' oversight duties.

The House Judiciary Committee had issued a subpoena to compel McGahn to testify Tuesday, and the committee's chairman, Rep. Jerrold Nadler, D-N.Y., has threatened to hold McGahn in contempt of Congress if he doesn't. Nadler has also suggested he may try and levy fines against witnesses who do not comply with committee requests.

McGahn's lawyer, William Burck, said in a letter to Nadler that McGahn is "conscious of the duties he, as an attorney, owes to his former client" and would decline to appear.

Still, Burck encouraged the committee to negotiate a compromise with the White House, saying his client "again finds himself facing contradictory instructions from two co-equal branches of government."

McGahn was a key figure in special counsel Robert Mueller's investigation, describing ways in which the president sought to curtail that federal probe. Democrats hoped to question him as a way to focus attention on Mueller's findings and further investigate whether Trump did obstruct justice.

"This move is just the latest act of obstruction from the White House that includes its blanket refusal to co-operate with this committee," Nadler said in a statement. "It is also the latest example of this Administration's disdain for law."

Separately on Monday, a federal judge in Washington ruled against Trump in a financial records dispute, declaring the president cannot block a House subpoena for information from Mazars USA, a firm that has done accounting work for him and the Trump Organization.

And a hearing is planned in New York on Wednesday in another case, this one involving an effort by Trump, his business and his family to prevent Deutsche Bank and Capital One from complying with subpoenas from two House committees for banking and financial records.

If McGahn were to defy Trump and testify before Congress, it could endanger his own career in Republican politics and put his law firm, Jones Day, in the president's crosshairs. Trump has mused about instructing Republicans to cease dealing with the firm, which is deeply intertwined in Washington with the GOP, according to one White House official and a Republican close to the White House not authorized to speak publicly about private conversations.

Administration officials mulled various legal options before settling on providing McGahn with a legal opinion from the Department of Justice to justify defying the subpoena.

"The immunity of the President's immediate advisers from compelled congressional testimony on matters related to their official responsibilities has long been recognized and arises from the fundamental workings of the separation of powers," the department's opinion reads. "Accordingly, Mr. McGahn is not legally required to appear and testify about matters related to his official duties as Counsel to the President."

The Judiciary Committee still plans on meeting even if McGahn doesn't show up and McGahn "is expected to appear as legally required," Nadler said.

Trump has fumed about McGahn for months, after it became clear that much of Mueller's report was based on his testimony. The president has bashed his former White House counsel on Twitter and has insisted to advisers that the attorney not be allowed to humiliate him in front of Congress, much as his former personal legal fixer Michael Cohen did, according to the official and Republican.

The Justice Department has long held the opinion that close presidential advisers have "absolute immunity" from being compelled to testify before Congress about their work for the president.

A federal judge rejected a similar argument in 2008 in a dispute over a subpoena for Harriet Miers, who was White House counsel to George W. Bush. U.S. District Judge John Bates said it was an unprecedented notion that a White House official would be absolutely immune from being compelled to testify before Congress. Miers had to show up for her testimony, but still had the right to assert executive privilege in response to any specific questions posed by legislators, the judge said.

But in 2014, under the Obama administration, the Justice Department issued an opinion arguing that if Congress could force the president's closest advisers to testify about matters that happened during their tenure, it would "threaten executive branch confidentiality, which is necessary (among other things) to ensure that the President can obtain the type of sound and candid advice that is essential to the effective discharge of his constitutional duties."

The House Judiciary Committee voted earlier this month to hold Attorney General Barr in contempt after he defied a subpoena for an unredacted version of Mueller's report.

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Associated Press writers Eric Tucker, Mary Clare Jalonick, Lisa Mascaro and Mark Sherman contributed to this report.