Mohamed Ghannouchi and Fouad Mebazaa, Tunisia's prime minister and president, have resigned from the (former) ruling Constitutional Democratic Rally (RCD) party of deposed president Zine El Abidine Ben Ali.
The move, announced on Tuesday, is seen as a concession to opposition cabinet members.
Earlier in the day, Tunisia's junior minister for transportation has said that he and two other ministers with ties to a top labour union have resigned from the newly formed government, leaving the new unity government in limbo.
Anouar Ben Gueddour said that he has resigned along with Houssine Dimassi minister of training and employment, and Abdeljelil Bedoui, a minister dealing with prime ministerial affairs. They are all members of a general national labour union.
Mustapha Ben Jaafar, the newly-appointed health minister, has also resigned.
Al Jazeera's Nazanine Moshiri, reporting from Tunis, said other members of the opposition in the cabinet threatened to resign unless certain conditions are met.
"They do not want to be in the government with certain members of the ruling party," said Moshiri.
The ministers' walkout comes a day after Mohamed Ghannouchi, the Tunisian prime minister, announced a new 'unity government', which eight high-ranking members of Ben Ali's government.
Monday's announcement of the new government was met with anger by some Tunisians, who said too many members of ousted president Zine El Abidine Ben Ali's party remain in power.
Ghannouchi said that the ministers remaining, who he says have "clean hands", had acted "to preserve the national interest."
Tunisians not happy with the new cabinet gathered on Tuesday to protest in the capital and several major cities.
Blake Hounshell, managing editor of Foreign Policy magazine, told Al Jazeera that it's clear that Ghannouchi made an error in reappointing so many ministers from Ben Ali's government.
"If you see what happened on the Tunisian streets today, the people who came out rejected the idea that the same old faces are going to still run the country,"said Hounshell.
"I think it remains to be seen whether this new government will even be able to stand and hold these elections in 60 days, as they're required to."
Tunisia's main trade union, which played a key role in protests against the North African state's ousted president, refused to recognise the new government.
The General Union of Tunisian Workers, better known under its French acronym UGTT, took the decision at an extraordinary meeting near Tunis.
In Tunis, riot police fired tear gas and clashed with protesters during a rally against the new government in the centre of the capital.
Al Jazeera's Nabeel Rihani, reporting from Tunis, said that security forces tried to prevent protesters from regrouping.
"There is news about similar protests in several major cities ... they are protesting the participation of the ruling party."
"Who did the revolt? It's the people, those trade union leaders ... they need to find their aspirations in the government. This government does not answer those aspirations," Masoud Ramadani, a workers union activist, told Al Jazeera.
Members of the interim government have defended its composition, however, saying that the members of the incumbent party who have been retained are not politicians.
Exiled leader returns
Moncef Marzouki, an exiled opposition leader and presidential hopeful, on Monday branded his country's new government a "masquerade" still dominated by supporters of ousted strongman Ben Ali.
"Tunisia deserved much more," the secular leftist declared.
"Ninety dead, four weeks of real revolution, only for it to come to this? A unity government in name only because, in reality, it is made up of members of the party of dictatorship, the CRD," Marzouki said.
Al Jazeera's Hashem Ahelbarra reported that Marzouki, a 65-year-old medical doctor and human rights activist, was met by a crowd on his supporters at Tunis airport on Tuesday.
Marzouki told them that he would ask Saudi Arabia to hand over Ben Ali to be prosecuted in Tunisia for "crimes committed against the people of Tunisia".
Rachid al-Ghannouchi (no relation to Mohamed Ghannouchi), the exiled leader of the Nahdha Movement party, told London-based Asharq Alawsat newspaper that leaders of his party had not been invited to participate in the negotiations in forming the so-called unity government.
He expressed anger at the exclusion, but said his party would consider joining the government if asked to do so.
Al Jazeera's Ahelbarra identified the lack of a coherent opposition as "one of the biggest problems that Tunisia faces for the time being".