Former national security adviser Michael Flynn asked a federal judge Tuesday evening for permission to withdraw his plea of guilty to lying to the FBI in special counsel Robert Mueller III’s probe of Russian election interference, alleging that prosecutors breached his cooperation agreement by demanding his false testimony.

The stunning reversal – more than two years after Flynn pleaded guilty Dec. 1, 2017, and just two weeks before he faces sentencing – threatens to sidetrack if not derail the prosecution of the highest-ranking Trump official charged and one of the first to cooperate with Mueller’s office.

Any change in plea must be approved by a judge.

In a 24-page filing, attorneys for Flynn alleged that after the former Army lieutenant general and adviser to President Trump switched defense teams last June, prosecutors for the first time demanded that Flynn falsely admit that he knowingly lied in filing forms with the Justice Department that hid his lobbying firm’s work for the government of Turkey.

“Michael T. Flynn hereby moves to withdraw his plea because of the government’s bad faith, vindictiveness, and breach of the plea agreement,” Flynn defense attorney Sydney Powell wrote.

Powell asked U.S. District Judge Emmet Sullivan in Washington to postpone Flynn’s sentencing until at least Feb. 27, “to allow time for the government to respond … and for Mr. Flynn to provide the additional briefing he needs to protect the record and his constitutional rights.”

The filing came one week after U.S. prosecutors recommended that Flynn serve up to six months in prison, reversing their earlier recommendation of probation after his attacks against the FBI and Justice Department.

The government revoked its request for leniency weeks after Sullivan rejected Flynn’s earlier claims that he had been duped into pleading guilty to lying to FBI agents about his Russian contacts after the 2016 U.S. election.

“It is clear that the defendant has not learned his lesson. He has behaved as though the law does not apply to him, and as if there are no consequences for his actions,” prosecutor Brandon Van Grack wrote in arguing that the government no longer considered his cooperation “substantial.”

Flynn, 61, pleaded guilty Dec. 1, 2017, to lying about his communications with then-Russian Ambassador Sergey Kislyak during the presidential transition.

In a cooperation deal, Flynn became a key witness in a probe into the administration which he served for 24 days, the shortest tenure of a national security adviser on record – before resigning in February 2017.

However, soon after Mueller’s investigation formally ended in March 2019, Flynn broke with the prosecutors who had credited him with helping them.

Flynn faces up to a five-year prison term under the charge, which included his misrepresentation of work advancing the interests of the Turkish government. However, ahead of Flynn’s initially scheduled sentencing in December 2018, prosecutors said he deserved probation for his “substantial assistance” in several ongoing investigations.

In a November 2018 filing, the special counsel’s office noted Flynn’s “early cooperation was particularly valuable because he was one of the few people with long-term and firsthand insight regarding events and issues under investigation.”

Flynn admitted to being in touch with senior Trump transition officials before and after his pre-inauguration communications with Kislyak, which involved efforts to blunt Obama administration policy decisions on sanctions on Russia and a United Nations resolution on Israel.

Prosecutors had earlier singled out Flynn’s “exemplary” public service, including 33 years in the military and combat service to warrant a possible sentence of probation.

Flynn’s attorneys joined that recommendation.

But at a Dec. 18, 2018, sentencing hearing, Sullivan lambasted Flynn’s attorneys for appearing to play down his offenses. Under questioning by the judge, Flynn repeated under oath that he admitted he was guilty as Sullivan recited at length his misstatements to Vice President Mike Pence, senior White House aides, federal investigators and the news media before and after Trump’s January 2017 inauguration about the nature of his foreign contacts.

“Arguably, you sold your country out,” Sullivan told Flynn, warning he might impose prison time. Flynn’s lawyers agreed to postpone the proceeding so that he could continue to show his good-faith cooperation.

This year Flynn switched defense lawyers, and his new team asked Sullivan to find prosecutors in contempt, alleging Flynn had been entrapped into pleading guilty and prosecutors wrongfully withheld evidence.