Former White House chief strategist Stephen Bannon was subpoenaed last week by special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE as part of the federal probe into Russian interference in the presidential election, The New York Times reported Tuesday.

Bannon, who joined the Trump campaign in August of 2016 and left the White House almost exactly a year later, is one of the few known instances that Mueller has used a subpoena to compel information from a member of President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE’s inner circle.

Mueller previously obtained subpoenas targeting former campaign chairman Paul Manafort Paul John ManafortOur Constitution is under attack by Attorney General William Barr Bannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention MORE, who has since been charged with a slate of federal crimes, including money laundering.

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Mueller interviewed dozens of Trump associates in the closing months of the year, but those individuals were not served with a subpoena, according to the Times.

It was not immediately clear why Bannon was treated differently. One source who would not be identified told the Times that Mueller would likely allow Bannon to forego the grand jury appearance and instead be interviewed by investigators in a less formal setting — suggesting that the move could be a negotiating tactic.

The revelation came as Bannon was appearing behind closed doors with the House Intelligence Committee to testify in that committee’s probe into possible collusion between the Trump campaign and Russia. He reportedly recently retained Bill Burck, of the law firm Quinn Emanuel.

The Mueller subpoena was handed down as Bannon has been in the spotlight over comments he made to Michael Wolff, the author of a controversial new book about the Trump White House.

The former official told Wolff that a June 2016 meeting at Trump Tower between campaign officials and a Russian lawyer believed to have political dirt on then-Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE was “treasonous.”

"The three senior guys in the campaign thought it was a good idea to meet with a foreign government inside Trump Tower in the conference room on the 25th floor—with no lawyers," Bannon said, according to Wolff’s account. “Even if you thought that this was not treasonous, or unpatriotic ... you should have called the FBI immediately.”

Further, Bannon added, “the chance that [Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE] did not walk these jumos up to his father's office on the twenty-sixth floor is zero.”

Lawmakers were expected to press Bannon on what the president knew about that meeting, long a flashpoint in the controversy surrounding the Trump campaign’s ties to Russia, as well as any financial crimes that may have been committed.

“Specifically what's the basis for his assertion that the president met with the participants in the Trump Tower meeting,” the committee’s top Democrat, Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE (Calif.), told ABC News's Pierre Thomas. “What [Bannon] knows about the president’s knowledge of that meeting, as well as his concerns over money laundering which has been a persistent concern of ours as well.”

But Bannon has limited first-hand knowledge into a number of key issues believed to be focal points of the Mueller investigation, including the Trump Tower meeting and the dismissal of FBI Director James Comey James Brien ComeyBook: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa Graham: Comey to testify about FBI's Russia probe, Mueller declined invitation MORE.

He was, however, reportedly involved in the decision-making behind firing former national security adviser Michael Flynn, who has since pleaded guilty to lying to federal investigators as part of the Mueller probe. Flynn was dismissed less than a month into the Trump administration after it was revealed that he had misled Vice President Pence on the nature of a phone call with the Russian ambassador.

The president broke publicly with Bannon after the publication of Wolff’s book, tweeting that “Sloppy Steve” has “been dumped like a dog by almost everyone.”

Updated at 12:17 p.m.