The retired federal judge appointed to argue against the Justice Department’s decision to drop its case against Michael Flynn, the former Trump adviser charged with lying to Congress during the Russia investigation, accused the DOJ of “gross abuse of prosecutorial power.”

In a 73-page brief, John Gleeson urged the department to continue its prosecution of Flynn.

Attorney General William Barr prompted backlash last month when his department intervened in the Flynn case and moved to drop charges.

“The reasons offered by the government are so irregular, and so obviously pretextual, that they are deficient,” Gleeson wrote. “Moreover, the facts surrounding the filing of the government’s motion constitute clear evidence of gross prosecutorial abuse. They reveal an unconvincing effort to disguise as legitimate a decision to dismiss that is based solely on the fact that Flynn is a political ally of President [Donald] Trump.”

Flynn twice pleaded guilty to lying to Federal Bureau of Investigation agents regarding his conversations with former Russian ambassador, Sergey Kislyak, shortly after Trump won the 2016 election.

The Justice Department said that Flynn should not have even been interviewed in the first place, since the FBI was about to close a portion of the investigation in which Flynn was under scrutiny for being a Russian asset.

Gleeson noted in his brief that the FBI does not require an investigation to have already established a basis for suspecting a counterintelligence threat before conducting voluntary interviews.

“The government may not enlist a court in dismissing a case solely because the defendant is a friend and political ally of the president — and where the ostensible reasons advanced for dismissal amount to a thin and unpersuasive disguise,” Gleeson wrote.

The Justice Department plans to file a response to Gleeson’s brief in the next few days.

In the meantime, Flynn’s lawyers and the Justice Department have asked the Court of Appeals for the District of Columbia Circuit to order the case against Flynn dismissed without further review.

They accused the federal judge overseeing the case, Emmet Sullivan, of abusing his power by appointing Gleeson to argue against dropping charges rather than going along with the DOJ’s move. They cited a 2016 opinion by the appeals court that said that the judiciary “generally lacks authority to second-guess” executive branch decisions about dropping cases.

An appeals panel will hear arguments on Friday about whether to allow Sullivan to conduct his review of the DOJ’s request to drop charges against Flynn.