Thousands of people marched in Paris on Tuesday to protest against a revamp of the debt-ridden pension system just ahead of a vote on the controversial measure in the National Assembly.
Similar rallies were held in other cities including Marseille, Toulouse and Lyon.
The protestors in Paris marched to the National Assembly, or the lower house of parliament, under a banner calling for "the creation of jobs, retirement at 60 and salary increases".
The National Assembly is set to vote on the reforms on Tuesday afternoon and it should be easily passed given that the ruling Socialists have a majority in the house.
After that it will be debated in the Senate from 28 October.
Pension overhauls are highly contentious in France. Previous attempts in 1995 and 2010 sparked mass protests and costly strikes but the Socialist government's latest reform has not yet met with the same level of resistance.
France is under pressure from the European Union and is seeking to plug holes that will see the generous state pension scheme fall into the red by more than 20 billion euros ($26.5 billion) by 2020.
The reforms will raise the pay-in period for pension contributions from the current 41.5 years to 43 years by 2035, meaning employees will need to work longer to be eligible for full pensions.
The plan also proposes increasing employee and employer contributions to France's retirement system, but avoids more controversial proposals such as raising the official retirement age from the current level of 62 or slapping a new tax on French retirees.
"The general logic of the reforms, especially the extension of the contribution period ...is socially very regressive," said Thierry Lepaon, the head of the CGT trade union.
Lepaon said the far-right National Front's recent win in a key by-election and projections that it will emerge as the biggest French party in European elections next year was proof of that.
"It's because there is despair," he said.