Attorney General William Barr is backing out of a hearing before the House Judiciary Committee on Thursday, escalating a fight with Democrats over the format of questioning.

“Unfortunately, even after the Attorney General volunteered to testify, Chairman Nadler placed conditions on the House Judiciary Committee hearing that are unprecedented and unnecessary," Kerri Kupec, a representative for the Justice Department, said in a statement to the Washington Examiner. "Congress and the Executive branch are co-equal branches of government, and each have a constitutional obligation to respect and accommodate one another’s legitimate interests. Chairman Nadler’s insistence on having staff question the Attorney General, a Senate-confirmed Cabinet member, is inappropriate.”

Chairman Jerry Nadler, D-N.Y., told reporters Wednesday evening that the Justice Department notified the panel that Barr will not testify about the federal Russia investigation. "Although we have worked around the clock to address his concerns, Attorney General Barr informed us he will not attend tomorrow's hearing," he said.

"Given his lack of candor in describing the work of the special counsel, our members were right to insist that staff be allowed to question the attorney general," Nadler insisted.

In a contentious meeting earlier in the day, the Democrat-led committee voted 21-14, along party lines, to permit to tack on an extra 60 minutes of questioning for staff lawyers to ask Barr questions, in addition to a round for lawmakers to grill him.

But Kupec said there was no good reason for this format, saying, "In light of the fact that the majority of the House Judiciary Committee – including Chairman Nadler – are themselves attorneys, and the Chairman has the ability and authority to fashion the hearing in a way that allows for efficient and thorough questioning by the Members themselves, the Chairman’s request is also unnecessary."

Since the weekend, Barr has threatened to pull out of the hearing if it strayed from the typical format. Barr faced questions about special counsel Robert Mueller's Russia investigation from Senate Judiciary Committee members on Wednesday. Lawyers were not involved.

Nadler had previously threatened the use of a subpoena to warn Barr against backing out. He gave no indication to reporters Thursday evening that Democrats would back down. "Given his lack of candor in describing the work of the special counsel, our members were right to insist that staff counsel be permitted to question the attorney general," he said, adding the Trump administration "cannot dictate the terms of our hearing."

The committee hearing will go on as planned at 9 a.m., and Nadler encouraged Barr to change his mind.

Nadler also said the Justice Department failed to comply with a subpoena that mandated Mueller's full, unredacted report be delivered to his committee by a Wednesday deadline.

Nadler said he will continue to work with Barr to get access to the full report and underlying evidence "but not for much longer." If DOJ can't reach an agreement in the coming days, Nadler said the "next step is seeking a contempt citation against the attorney general."

In a letter sent to Nadler on Wednesday, Assistant Attorney General Stephen Boyd said the subpoena for full access to Mueller's findings, including grand jury information, was "not legitimate oversight.”

The panel's top ranking member, Doug Collins, R-Ga., railed against the format as a de facto impeachment proceeding against President Trump. "The precedent for staff questioning is impeachment, but the problem is they can't bring themselves to bring impeachment," Collins said at the time of the vote. "[They] want the appearance of impeachment to satisfy the base, to talk to others, to impugn integrity, to do whatever to smear the president ahead of the 2020 election."

Reacting to Barr not planning to testify on Thursday, Collins accused Nadler of choosing to "torpedo our hearing."

Barr's appearance before the GOP-controlled Senate Judiciary Committee gave Democrats more ammo to condemn the attorney general, who have already been very critical of his rollout of Mueller's report.

In a line a questioning with Sen. Kamala Harris, D-Calif., Barr admitted that he decided not to charge Trump with obstruction of justice without seeing the underlying evidence of Mueller's Russia investigation report.

Harris and other 2020 presidential candidates have seized on Barr's testimony and a newly revealed letter for Mueller to Barr criticizing the attorney general for a summary of the investigation's "principal conclusions," and called on him to resign. She joins a long list of Democrats saying they'd lost confidence in Barr and questioning his continued fitness for the job.

Kupec defended Barr's performance. “Today, the Attorney General testified before the Senate Judiciary Committee for over five hours. The Attorney General also voluntarily released the Special Counsel’s confidential report with minimal redactions to Congress and the public, made an even-less redacted report available to Chairman Nadler and congressional leadership (which they have refused to review), and made himself available to the Committee by volunteering to testify this week," she said.

“The Attorney General remains happy to engage directly with Members on their questions regarding the report and looks forward to continue working with the Committee on their oversight requests," Kupec said.