"We call on Tunisians to boycott this illegal, unconstitutional process that aims to legitimize a coup d'etat," veteran opposition figure Ahmed Nejib Chebbi, leader of the National Salvation Front, told AFP.
Chebbi told reporters that rights and freedoms in the North African country would be threatened if the charter was approved.
"For me it's the quintessential bad constitution," he said.
Jawhar Ben Mbarek, National Salvation Front (FSN) member and leader of "Citizens Against the Coup", urged Tunisians on Monday to "massively reject this referendum".
"We reject the entire process," he told AFP. "We are committed to the 2014 constitution, which we consider to be the only legal constitution, representative of the will of the Tunisian people."
The process of writing the constitution has come under fire. along with the document.
The legal expert who oversaw the constitution's drafting has disavowed it, saying it was "completely different" from what his committee had submitted and warning that some articles could "pave the way for a dictatorial regime".
Then last week, Saied published an amended draft, apparently attempting to ward off criticism after the original was blasted for the nearly unlimited power it gave his office.
The draft constitution up for referendum is the centerpiece of Saied's program to overhaul Tunisia's political system, but rivals say the text confirms fears he is seeking to reinstall an autocracy.
"We call on Tunisians to boycott this illegal, unconstitutional process that aims to legitimize a coup d'etat," veteran opposition figure Ahmed Nejib Chebbi, leader of the National Salvation Front, told AFP on the sidelines of a news conference in Tunis.
Chebbi told reporters that rights and freedoms in the North African country would be threatened if the charter was approved.
"For me it's the quintessential bad constitution," he said.
The National Salvation Front (FSN) includes five political parties, among them Saied's nemesis the Islamist-inspired Ennahdha party, along with five civil society groups involving independent political figures.
It was formed in April, months after Saied, a former law professor elected in 2019 amid public anger against the political class, on July 25, 2021 sacked the government and suspended parliament, later seizing far-reaching legislative and judicial powers.
The European Union called Monday for an "inclusive national dialogue", saying it would be "a cornerstone of any credible constitutional process and long-term stability".
"It is essential to bring together the widest possible spectrum of political and societal actors in addressing the political, economic and social challenges the country is facing," EU foreign policy chief Josep Borrell's office said in a statement.
