The new demonstrations planned for Tuesday follow student and labour union rejection the French president's bid to soften the blow of a jobs law that would make it easier to fire young workers.
Jacques Chirac signed the law on Sunday but urged that it not be applied until a new, softer version is devised with two key modifications that take opponents' concerns into account.
The law was aimed at stemming youth unemployment. Opponents want it repealed, not watered down.
Bruno Julliard, head of a leading students' union, told France Inter radio on Monday: "We are on the edge of victory."
Dismissing talk that students' forthcoming spring vacation could deflate the protest movement, he said: "The determination of youth is at a high level."
Dominique de Villepin, the French prime minister, convened his government on Monday to consider France's stagnant job market and soaring youth unemployment.
Villepin, who devised the law and has been devastated by the fury against it, sought to show that he is still in charge of a government increasingly threatened with fracture over the measure.
Strongest possible turnout
Bernard Thibault, head of the CGT union, said on RMC radio that he hoped for "the strongest possible" turnout on Tuesday. Unions expect the protests to match a similar action last week that brought at least one million people to the streets.
Paris was deploying about 4,000 police to keep order during the protest in the capital, one of about 150 planned around the country, the police department said.
Other recent demonstrations over the law have turned violent.
On Monday, protesters disrupted air, train and car traffic.
Flights in and out of Paris' Orly airport were delayed as the civil aviation authority prepared for Tuesday's disruptions.
Students blocked major highways near Paris and Lyon, in the southeast, snarling traffic for several kilometres.
Protesters also blocked rail traffic in Rouen in the northwest.
A handful of members of the Green Party staged a sit-in Monday at the Sorbonne university, which has been shuttered for weeks.