Lawyers and judges across the country as well as teachers at Mandouba university, near Tunis, kicked off a two-day strike in response to the killing of Chokri Belaid outside his home on Wednesday, officials said.
The influential labor union, UGTT, meanwhile, was meeting to decide its course of action in the wake of the killing.
Police deployed in numbers in the capital's Habib Bourguiba Avenue, epicenter of the 2011 uprising that toppled ex-dictator Zine El Abidine Ben Ali, and where thousands had gathered Wednesday in scenes reminiscent of the revolution.
Security trucks, buses and vans were visible around the city center and roads near the interior ministry were closed to traffic.
Shops reopened in the area, but many of them kept their shutters down to protect their windows.
While opposition parties and unions refrained from calling people onto the streets Thursday, spontaneous protests that erupted in a dozen towns and cities the previous day served as a reminder that social upheaval remains a real threat.
One policeman was killed after being hit by rocks in Tunis, while protesters torched and ransacked offices of the ruling Islamist Ennahda party in a number of towns as news spread of Belaid's assassination.
Ennahda has been squarely accused by Belaid's family of being behind the killing, which was carried out by a lone gunman -- charges it vigorously denies.
Prime Minister Hamadi Jebali, who hails from Ennahda, said in a televised address on Wednesday that he would form a new administration of non-political technocrats ahead of fresh elections.
"I have decided to form a government of competent nationals without political affiliation, which will have a mandate limited to managing the affairs of the country until elections are held in the shortest possible time," he said.
Jebali did not specify that he was dissolving the existing government, nor did he set a date for the reshuffle which must be confirmed by the national assembly.
Tunisian media voiced fears that the murder of Belaid, a prestigious leftist opposition figure and outspoken critic of the ruling Islamists, could plunge the country into a new cycle of violence.
The killing comes at a time of rising violence in Tunisia stoked by political and social discontent two years after the mass uprising that forced Ben Ali to flee and touched off the so-called Arab Spring.