Tunisia's ruling Islamist Ennahda party and the opposition called rival rallies for Tuesday to mark national women's day, reflecting deepening divisions in the North African country.
The country is in the grip of a political crisis sparked by the murder of an opposition politician last month, the second such killing this year.
Ennahda chief Rached Ghannouchi met Houcine Abassi, head of the powerful UGTT trade union confederation to discuss the crisis and the talks continued well into the night.
The UGTT, which has backed some but not all of the opposition's demands, has been touted as a possible mediator between the Islamist-led government and the opposition.
Critics of the government are calling for demonstrations on Tuesday evening to defend women's rights followed by a march outside parliament, where the opposition has held nightly demonstrations since the July 25 assassination of opposition MP Mohamed Brahmi.
Tuesday is the 57th anniversary of the Personal Status Code that was adopted on August 13, 1956, giving Tunisian women rights unequalled in the Arab world at the time.
Critics of Ennahda, including the UGTT, charge that those rights are now under threat from the Islamists.
"This will be a historic demonstration given the difficult circumstances the country is going through: political killings, terrorism and attempts to roll back women's rights," UGTT official Najoua Makhlouf told a news conference.
Amel Radhouani, from the Femmes Libres (Free Women) group said the march would send a clear message to the Islamists in power.
"This will not be a celebration but a march against terrorism, and Ennahda's attempts to take back women's gains," Radhouani said.
Critics say Ennahda has been too passive in dealing with radical imams who have called for the return of polygamy and child brides -- traditions banned in Tunisia under the 1956 law.
The party drew further criticism last year when it called for sexual equality to be replaced in Tunisia's new post-revolution constitution by "complementarity" of the genders.
But Ennahda strongly denies it is against women's rights and called on its supporters to gather from 1500 GMT on Tuesday in the capital's Habib Bourguiba Avenue, epicentre of the 2011 uprising that toppled veteran strongman Zine El Abidine Ben Ali.
The party said the rally would be held under the slogan: "Tunisia's women, pillars of the democratic transition and national unity".
Sexual equality has been one of the stumbling blocks to achieving consensus on the much delayed post-revolution constitution.
The speaker of the National Constituent Assembly, Mustapha Ben Jaafar, last week suspended work on drafting the new charter until the government and the opposition hold talks to resolve their differences.
Opposition members of the assembly have been boycotting its sessions since Brahmi's murder.
But Ennahda and its coalition partners, including the centre-left President Moncef Marzouki, on Monday rejected the speaker's action as "illegal" and called for the assembly to resume it work on Wednesday.
Ennahda has offered to broaden the governing coalition in the run-up to elections it hopes can be held in December after the completion of the new constitution and electoral law.
But it has rejected opposition calls for it to step down immediately and for the constituent assembly to be dissolved.
It has also rejected the appeals of both the UGTT and employers' organisation UTICA for it to hand over to a government of technocrats.
As the political crisis has deepened, the army has been engaged in a two-week offensive against Al-Qaeda-linked militants near the Algerian border.
On Monday, troops recovered the bodies of six suspected militants on Mount Sammama, which has been the target of multiple air strikes, a military source told AFP.
The mountain lies to the northeast of the Chaambi Massif, where the bodies of eight soldiers were found with their throats slit after an ambush on July 29.