The Vatican’s disciplinary body, the Dicastery of the Doctrine of the Faith, issued a formal decree, made public by Viganò on Thursday, assigning the senior cleric to a penal canon trial. The charges: the “crime of schism” and “denial of the legitimacy of Pope Francis.”

Such trials are exceedingly rare, and the move underscores a recent effort by the Vatican to take more formal action against a gaggle of archconservatives who have sought to undermine Francis’s papacy from the inside. Conviction could lead to Viganò’s defrocking and excommunication. It would end the long career of the 83-year-old Italian cleric who has emerged as the leading symbol of a traditionalist resistance to a papacy perceived by him as wildly liberal.

On Thursday, Viganò said in a statement that he saw the “accusations against me as an honor.” He referred to Francis as he always does, eschewing his official title and using his name before he was pope: Jorge Mario Bergoglio.

“It is no coincidence that the accusation against me concerns the questioning of the legitimacy of Jorge Mario Bergoglio and … the ideological, theological, moral, and liturgical cancer of which the Bergoglian ‘synodal church’ is the necessary metastasis,” Viganò wrote.

Viganò hasn’t made many public appearances since calling for Francis’s resignation in 2018. But he has continued to deliver stinging missives on X and the conservative U.S. outlet LifeSiteNews. He has also talked about creating a seminary free of Vatican interference.

Francis has for years tolerated open dissent, including vitriolic attacks from within clerical ranks. But as criticism has grown louder in recent months, the Vatican has taken more decisive action. Bishop Joseph Strickland of Tyler, Tex. was stripped of his diocese, while American Cardinal Raymond Burke, who frequently spoke at conservative conferences that excoriated Francis, lost his pension and Rome apartment.

It’s possible that the most severe punishment has been reserved for Viganò.

He was ordered to appear at the Vatican’s disciplinary office on Thursday and told that he would be tried in absentia if he didn’t, according to document advising him of the charges. It was not clear if he had presented himself after publicly signaling his defiance.

On Thursday, that Vatican’s secretary of state, Cardinal Pietro Parolin told journalist in Rome that “Archbishop Viganò has taken some attitudes and some actions for which he must answer.”

“I am very sorry because I always appreciated him as a great worker, very faithful to the Holy See, someone who was, in a certain sense, also an example. When he was apostolic nuncio he did good work.

“I don’t know what happened,” the Parolin said.