Four Tunisian parties said on Thursday that President Kais Saied has lost his legitimacy and called for an end to what they called a coup after he took control of legislative and executive powers.
Saied said on Wednesday he would rule by decree and ignore parts of the constitution as he prepared to change the political system.
Attayar, Al Jouhmouri, Akef and Ettakatol parties said in a joint statement that Saied's move enshrined an absolute power monopoly.
Saied has held nearly total power since July 25 when he sacked the prime minister, suspended parliament and assumed executive authority citing a national emergency.
Thursday's opposition statement increased the pressure on him. Although the four parties are not the most powerful, they hold influence in the streets, especially Attayar, which was close to Saied before his intervention.
"We consider the president has lost his legitimacy by violating the constitution.. and he will be responsible for all the possible repercussions of this dangerous step," the four parties said in the statement.
Anour Ben Kadour, a senior official in the powerful UGTT labour union, said: "Tunisia is heading towards absolute, individual rule."
UGTT, which has about one-million members and is a major force in Tunisian politics, has started a meeting to formulate a position on Saied's actions and is expected to issue a statement on Thursday.
While many Tunisians have backed Saied and see his actions as necessary to oust a corrupt and unpopular political elite after years of economic stagnation, his critics from across the spectrum say he is inexperienced and uncompromising.
The leader of Tunisia's powerful Islamist Ennahda party, Rached Ghannouchi, said on Wednesday that Saied's declarations meant cancelling the constitution. The party - the biggest in parliament - would not accept that, he said.
Saied's moves have undermined the democratic gains of Tunisia's 2011 revolution that ended autocratic rule and triggered the Arab Spring, despite his pledges to uphold the freedoms won a decade ago.