A U.S. judge put on hold the Justice Department’s move to drop charges against Michael Flynn, saying he expects independent groups and legal experts to argue against the bid to exonerate President Trump’s former national security adviser of lying to the FBI.

U.S. District Judge Emmet G. Sullivan said in an order Tuesday that he expects individuals and organizations will seek to intervene in the politically charged case. Having others weigh in could preface more aggressive steps that the federal judge in Washington could take, including — as many outside observers have called for — holding a hearing to consider what to do.

Sullivan’s order came after the government took the highly irregular step Thursday of reversing its stance on upholding Flynn’s guilty plea.

The action by Sullivan, a veteran 72-year-old jurist with a national reputation for advocating defendants’ rights to full government disclosure of evidence, appears to rule out immediate action on the Justice Department’s decision to reverse course and throw out Flynn’s December 2017 guilty plea.

Sullivan said he will “at the appropriate time” set a schedule for outside parties to argue against the Justice Department’s claims as the government seeks to drop the charges.

Such “friend-of-the court” or “amicus brief[s] should normally be allowed when a party is not represented . . . has an interest in some other case that may be affected . . . [or] has unique information or perspective that can help the court,” Sullivan said.

The judge said he would be a rigorous gatekeeper, adding, “A criminal proceeding is not a free for all.”

A Justice Department spokesperson did not immediately respond to a request for comment.

In an immediate written response to the court, Flynn’s defense said the order was prompted by a notice Monday from an unspecified group referring to itself as “Watergate Prosecutors” that sought to file arguments in the case.

“No rule allows this filing,” Flynn attorney Sidney Powell objected.

Powell said in the more than two years of Flynn’s prosecution, “This Court has consistently — on twenty-four (24) previous occasions — summarily refused to permit any third party to inject themselves or their views into this case.”

Powell also challenged the constitutionality of Sullivan’s order, saying the courts have no authority to permit a third party to “usurp the role of the government’s counsel” in prosecuting an individual in a criminal case.

“This travesty of justice has already consumed three or more years of an innocent man’s life — and that of his entire family,” Powell wrote. “No further delay should be tolerated or any further expense caused to him and his defense.”

The judge’s ruling appeared to be prompted by a unique request filed one day earlier by the team of Watergate prosecutors who pursued an investigation of President Richard Nixon. They sought to file a friend-of-the-court brief to give their legal arguments against Barr’s unusual reversal of Flynn’s prosecution and said they had a “unique perspective on the need for independent scrutiny and oversight to ensure that crucial decisions about prosecutions of high-ranking government officials are made in the public interest.”

“The integrity of prosecutorial decision making is a cornerstone of the rule of law,” they wrote. “Amici have a special interest in restoring the public trust in prosecutorial decision making and in public confidence in the viability of future independent investigations and prosecutions if the results of such work are likely to be subjected to reversal by transparent political influence.”

Sullivan’s order noted that he was proceeding under a rule of civil procedure that gives judges sole discretion to accept outside arguments. Although there is no parallel criminal rule, the federal appeals court for Washington has ruled external entities in criminal cases can always ask to file an amicus brief, Sullivan said.

Legal experts said the order allows others to file objections to the Justice Department’s move and could open the door for adversarial proceedings in which one or more attorneys argue against the Justice Department. It would also permit, if the judge chooses, requiring both sides to produce evidence and revisit the case for and against Flynn.

In an evidentiary hearing, Sullivan could call witnesses — such as Flynn, his investigators or even prosecutors — to obtain more facts about how the case was handled and why Flynn and agents took the steps they did.

Sullivan has not hesitated to personally question Flynn in court before, as he did during a 2018 hearing, when he rejected a defense motion supported by the government for probation.

Sullivan had said he was not satisfied by the former three-star Army general’s cooperation with special counsel’s probe.

“Arguably, you sold your country out,” Sullivan told Flynn.

Flynn was convicted of lying to investigators about his contacts with Russia’s ambassador about easing U.S. sanctions during Trump’s presidential transition in special counsel Robert S. Mueller III’s investigation of interference in the 2016 election.

Flynn had initially repeated that he was guilty of lying, that no one had coerced him to admit his guilt and that he had no intention of taking back that plea. Flynn also said he took responsibility for wrongdoing that also culminated in his firing by Trump for misleading Vice President Pence, White House aides and the public.

After Mueller’s investigation into 2016 campaign interference closed last year, Flynn changed defense teams, began attacking prosecutors and gained Trump’s support, claiming he was entrapped in a partisan FBI and Justice Department conspiracy.

In January, Attorney General William P. Barr tapped Jeff Jensen, the U.S. attorney in St. Louis, to review how the case had been handled. Jensen said publicly last week that he recommended it be dropped. Jensen asserted that newly analyzed FBI reports and communications showed the bureau had no valid basis to question Flynn, so any lies he told were not relevant to a criminal probe.

The Justice Department’s attempts to dismiss the case last week prompted fresh accusations from law enforcement officials and Democrats that the criminal justice system was caving to political pressure from the Trump administration.

Flynn prosecutor Brandon Van Grack, a Mueller team member, quit the case in apparent protest before the Justice Department’s move to drop the charges, while Trump applauded the actions.

Matt Zapotosky contributed to this report.