Governments using the coronavirus crisis to stage an executive power grab would be "politically dangerous, and morally unacceptable," said Donald Tusk, the leader of Europe's center right political grouping, in a thinly-veiled attack on Hungary's Prime Minister Viktor Orbán.

In a letter to European People's Party staff, the former European Council president said the crisis should not be used as an excuse for state overreach.

"The state of emergency, or the state of danger, must serve the governments in their fight against the virus, and not strengthen their power over the citizens," Tusk wrote in the letter, seen by POLITICO. "Making use of the pandemic to build a permanent state of emergency is politically dangerous, and morally unacceptable."

"This is why so many questions and concerns appear regarding the situation in Hungary, where according to many, the emergency measures which have been introduced are disproportionate and inadequate, and what is more, they have been introduced for an indefinite period of time," he added.

Orbán's move to rule by decree indefinitely in order to fight the virus — which was endorsed on Monday by a two-thirds majority in the Hungarian parliament — has drawn widespread criticism, including from U.S. Republican politicians. But up to now top officials in the EPP, which has Orbán's Fidesz party as a member, have remained silent.

Orbán accused Tusk of using the EPP as a "playground for his Polish domestic political games."

Tusk's letter, which he subsequently released publicly, follows one dated March 27 and seen by POLITICO from the Hungarian leader to Annegret Kramp-Karrenbauer, the leader of Germany's Christian Democratic Union party. The CDU is the party of German Chancellor Angela Merkel and influential in the EPP.

In his letter, Orbán accused Tusk of using the EPP as a "playground for his Polish domestic political games." He urged Kramp-Karrenbauer to "persuade President Tusk to stop sowing the seeds of division in our political family and to start focusing on what is needed right now."

Accusing Tusk of aligning himself with the liberals and the left, Orbán wrote that "those who are unable to help should at least refrain from hindering the efforts of others. This is not a game. The lives of our citizens are at stake in every member state."

EPP members have been growing increasingly concerned about the perceived authoritarian tendencies of Orbán's government. The political grouping suspended Fidesz last March over concerns about the rule of law in Hungary and Orbán's clashes with EU institutions over migration and other issues. But since then, the EPP has struggled with how to address ideological divisions between its moderate and right-wing factions. Last February, its annual political assembly decided to prolong the suspension rather than expel Orbán's party.

In his letter, Tusk suggested that Orbán's latest move would demand a rethink. "Many of you, even if you criticized PM Orbán for his previous decisions, did not agree to expel FIDESZ from our political family," Tusk wrote. Even though the priority is to fight the Coronavirus outbreak, Tusk said "the time will soon come, when you will have to again re-consider your positions."

Tusk does not have the power to expel Fidesz himself. That decision rests with the EPP's political assembly, which brings together senior leaders of the party and the group in the Parliament. The next political assembly is planned for June.

Orbán's emergency law appears to have outraged even those who had been more muted in their criticism of the Hungarian leader.

“People in the middle have been pushed to get rid of Fidesz,” said one EPP staffer, who noted that many MEPs were “upset” with Hungary’s latest law. The staffer said there was sympathy toward Tusk, who is "respected and liked" within the party.

“Excellent news," said Finnish MEP Petri Sarvamaa in response to Tusk's letter. "This will hopefully make those hesitant inside the EPP group about dismissing Fidesz to reconsider their positions.”

Earlier on Wednesday, Danish MEP Pernille Weiss sent a letter to Tusk noting that her Conservative People’s Party of Denmark "believes the time has come to take the necessary initiative and expel Fidesz from the group in the European Parliament and the EPP Party."

"We believe that the EPP has shown the required patience with Fidesz and should show credibility towards the millions of European citizens who have cast their vote for the EPP," the letter said.