A series of battles between Trump administration officials and congressional Democrats escalated over the weekend as one high-profile Cabinet member threatened to boycott a scheduled hearing and another official was facing the threat of contempt proceedings.

Attorney General Bill Barr has been slated to appear before the House Judiciary Committee on Thursday to testify on the process behind the release of Special Counsel Robert Mueller’s report, but it is unclear at this point if he will attend. Fox News learned over the weekend that Chairman Jerrold Nadler, D-N.Y., wanted to have committee staff question Barr on his handling of the report.

But Barr wants lawmakers to do the questioning and, according to a source close to the committee, has said he will not come in to testify based on where things currently stand.

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“The Attorney General agreed to appear before Congress. Therefore, Members of Congress should be the ones doing the questioning,” Justice Department spokeswoman Kerri Kupec told Fox News. “He remains happy to engage with Members on their questions regarding the Mueller report.”

Nadler fired back Monday, saying the attorney general is "afraid" to subject himself to additional questions.

Discussions are ongoing, and it's unclear if they might reach a resolution. A spokesperson for committee Republicans called Democrats' demands “abusive and illogical.”

“Attorney General Barr wasn’t asked to testify before the committee—he offered. He provided the Mueller report voluntarily. He invited Democrat leaders to view the less redacted report in person. Yet the only thing, apparently, that will satisfy Democrats, who refuse to read the less redacted report, is to have staff pinch hit when a cabinet-level official appears before us,” the spokesperson said.

Is it unusual for committee counsels to question a witness, but committees generally can make their own rules. Other panels have made similar exceptions.

Barr has faced heated criticism since last month when he released an initial four-page summary of Mueller’s findings. Barr stated that the special counsel found no evidence of collusion between members of the Trump campaign and Russia during the 2016 presidential election. Mueller also led an inquiry into whether the president obstructed justice in the investigation, but ultimately did not come to a conclusion on the matter. Instead, Barr and Deputy Attorney General Rod Rosenstein announced that the evidence found in the probe was not sufficient to charge the president with an obstruction of justice offense.

Democrats have questioned that conclusion, especially after Barr released the nearly 500-page report recounting numerous incidents of Trump allegedly trying to curtail the probe. Democrats also objected to the redactions made in the report issued to the public.

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“He is attorney general of the United States of America, not the attorney general of Donald Trump,” House Speaker Nancy Pelosi, D-Calif., said earlier this month.

Meanwhile, a separate battle has developed over the testimony of ex-White House security official Carl Kline. House Oversight Committee Chairman Elijah Cummings, D-Md., subpoenaed Kline earlier this month to appear before the panel as part of its investigation into the issuing of security clearances at the White House. But last week, the White House blocked Kline’s testimony.

The White House told Kline to defy the subpoena and said Kline could not testify unless a member from the White House counsel’s office was present. The White House made that request to Cummings, but was denied.

On Friday, committee Ranking Member Jim Jordan, R-Ohio, warned the White House that Cummings could initiate contempt proceedings against Kline should he not appear. Jordan requested that Kline come for a transcribed interview with committee staff. A source close to Jordan told Fox News Friday that the move was “in an attempt to get Kline’s testimony, not to head off contempt, but to de-escalate, respect the process, and get information.”

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The White House has since opened the door to a limited interview. In a letter over the weekend, Cummings scheduled one for Wednesday morning but said the scope will not be limited -- and reiterated his contempt threat in stark terms.

“Based on the record before us, I am confident that the Committee could move forward with contempt against you immediately, particularly since your defiance of the Committee’s subpoena was so flagrant,” Cummings wrote. “... You will be expected to answer all of the Committee’s questions, including questions about specific White House officials and allegations of retaliation against the whistleblower. If you answer all of these questions, there would be no need for the Committee to pursue contempt against you in the future. This burden rests squarely with you, with the advice of your personal counsel, and not with White House attorneys who may direct you to disregard the Committee’s questions without an assertion of privilege.”

The probe intensified after Tricia Newbold, an 18-year government employee who oversaw the issuance of clearances for some senior White House aides, revealed that she compiled a list of at least 25 officials who were initially denied security clearances last year, but had senior officials overrule those denials.

The clash between the White House and Congress is escalating on other fronts as well. The president, last week, vowed to fight all subpoenas for current and former Trump administration officials.

“We’re fighting all of the subpoenas,” Trump said last week. “Look, these aren’t like, impartial people. They are Democrats trying to win in 2020. …They’re not going to win against me.”

He added that “the only way they can luck out is by constantly going after me on nonsense.”

In a separate push, top Democrats on several House committees launched an investigation into the massive shakeup in leadership at the Department of Homeland Security, citing allegations that the president removed top officials for refusing to carry out his desired immigration policies. The first witness the panels called was White House adviser Stephen Miller, but the White House blocked his testimony as well.

White House Counsel Pat Cipollone notified Cummings that Miller would decline the invitation, and instead, offered cabinet secretaries and other agency officials to appear instead.

Also last week, the House Judiciary Committee subpoenaed former White House Counsel Don McGahn, whose testimony, likely related to Mueller’s obstruction inquiry, was also blocked by the White House.

Trump, last week, called the McGahn subpoena “ridiculous,” and also touted his administration’s transparency.

“I let everybody testify. There’s never ever been transparency like this,” Trump said. “With all of this transparency, we finished. No collusion, no obstruction…But then I get out, the first day, they say, ‘let’s do it again.’ I say, that’s enough, we have to run a country. We have a very great country to run.”

Fox News' Mike Emanuel, Gregg Re, and Kristin Brown and The Associated Press contributed to this report.