French President Francois Hollande has insisted that a controversial labour reform will not be withdrawn as strike action on the railways.
“The text assures the best performance for businesses and offers new rights to employees,” he told a newspaper.
Protesters clashed with police last week during marches against the bill, which makes hiring and firing easier.
There are concerns the Euro 2016 football championships, which France hosts next week, may be disrupted.
Tourism chiefs in Paris have warned that the unrest is putting off visitors to one of the world’s top destinations.
According to the tourist board, “the scenes of guerrilla-type action in the middle of Paris, beamed around the world, reinforce the feeling of fear and misunderstanding.”
The capital’s reputation as a safe destination was already dented by November’s deadly attack by militants from the self-styled Islamic State (IS) group, who killed 130 people in gun and bomb attacks.
Meanwhile, thousands of public sector workers in Belgium are taking part in a 24-hour national strike against budget cuts, changes to working hours and a rise in the retirement age.
Police officers, teachers and some civil servants are joining train drivers and prison guards already on strike.
A national railway strike is due to get under way in France on Wednesday, according to an announcement by the state rail company SNCF (in French).
According to the French daily Le Monde, “strike action will actually begin at 19:00 (17:00 GMT) on Tuesday while another paper, Le Figaro, said it would start at 20:00.”
The Paris Metro is due to go on strike from Thursday, and six of the country’s eight oil refineries are still halted or running at reduced capacity due to union action.
Air France pilots have voted to strike for at least six days in June in a separate dispute over productivity targets.
The labour reform, which is aimed at making the labour market more flexible, was pushed through the lower house of parliament without a vote.
A new national day of action is planned by unions for 14 June, when the bill goes to the Senate.
Labour Minister Myriam El Khomri said on Tuesday that she was waiting to hear from the CGT, the union leading the action, after hearing that its leader, Philippe Martinez, had called for new talks.