Some 221 protest actions are planned in cities and towns across the country, most notably in Paris, Marseilles, Lyon, Toulouse, Lille and Nantes, French media estimated. Up to 80,000 people are expected to rally in the capital alone.
French government spokesman Olivier Veran urged those planning to take part in the strikes not to disrupt French people's daily life during the protests.
"Tomorrow, there will be a general mobilization at the call of trade unions. This protest corresponds to a democratic expression of opinion that we respect. We hope that the protest action will not turn into a 'blocking' of the country," Veran told a government briefing.
Trade unions have called for action in solidarity against the government's plans to raise the retirement age to 64 from 62, end pension advantages in some industries and increase the number of years needed to receive full retirement benefits. The reform still needs parliamentary approval.
Workers from the energy industry, public transport and teachers will stage one day walkouts. The strike will impact rail and air traffic, with one in five flights being canceled on Thursday at the Orly international airport in Paris.