At its heart is President Azali Assoumani, facing a mounting chorus from critics who describe him as bent on enshrining himself in power and destroying democracy.
The Constitutional Court has been suspended, demonstrations outlawed and one of Azali's leading critics, former president Ahmed Abdallah Sambi, has been placed under house arrest.
A referendum on a package of so-far unconfirmed constitutional changes is due on July 29. Azali has also indicated he will call elections next year, which could enable him to remain in office beyond 2021, when his currently non-renewable term expires.
"It's a constitutional coup d'etat," said Youssouf Boina, head of the opposition Union for the Development of the Comoros (UPDC) party.
"Azali has set in place a war machine to carry out his personal ambitions," said the head of the Juwa party, Ahmed el-Barwane.
Among grassroots groups, Salim Soulaimana, president of the Federation of Civil Society Organisations (Fecosc), expressed alarm.
"We are bidding farewell to the republic and becoming a monarchy in all but name," he said.
History of turmoil
The Comoros -- an archipelago of three islands between Mozambique and Madagascar and one of the world's poorest countries -- has had a long history of political turmoil, including intervention by mercenaries, since it gained independence from France in 1975. A fourth island in the group, Mayotte, remains part of France.
Azali, a 59-year-old former colonel, was president between 1999 and 2002, coming to power after ousting acting president Tadjidine Ben Said Massonde in a military coup.
He won the election three years later, stepping down in 2006 to democratically hand over power to Sambi. But in May 2016, he returned again as president after an election marred by violence and allegations of voting irregularities.
On May 19, Sambi, president from 2006-11, was placed under house arrest at his home near the capital of Moroni, just days after he had returned to the Comoros from a six-month absence abroad.
"Acts like these put our democracy under threat," Sambi retorted. "We no longer have the right to meet, to express ourselves, to move."
The aim of the move was "to provoke," Sambi continued. "It's as if they want to lead us into crisis."
The move appears to be linked to an incident a day before when Azali and Sambi both attended Friday prayers, and as they left Moroni's main mosque, Sambi's supporters jeered Azali.
The interior ministry said the move was imposed to "preserve public order and security," accusing Sambi of behaviour that fomented "stone-throwing at the police, violent demonstrations and disruption to religious ceremonies."
Several hundred Sambi supporters demonstrated outside the mosque on Friday to demand that he be freed from house arrest, an AFP journalist reported.
In addition to Sambi's house arrest, the authorities have ordered that anyone seeking to preach "obtain the consent of the ulemas," a body of religious scholars, in Moroni -- an apparent jab at Sambi, who frequently makes sermons.
Accusations that the government is cracking down on freedom of expression raise official hackles.
"We are only applying the measures that were approved during the Sambi presidency but which were never used," Interior Minister Mohamed Daoudou told AFP. "Now that they are (being applied), people are saying it's a dictatorship."
Sambi's party, Juwa, also complains that it was barred from holding its congress at a large venue in Morono, and accuses police of using teargas to break up a rally on his home island, Anjouan.
In April, Azali suspended the Constitutional Court -- his spokesman, Mohamed Ismailla, said the institution had become "useless, superfluous and incompetent" because the eight-seat panel only had three judges and thus could not constitute a quorum.
"All that was needed was to appoint judges" to achieve a quorum and make it operational, one of the court's members, Soidri Salim Madi, said.
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