France's government has proposed raising the legal retirement age from 62 to 64 by 2030 in a major reform to the pension system.
PM Elisabeth Borne said the changes were necessary to prevent a major deficit in the system in the future.
Reforming pensions was one of President Emmanuel Macron's main promises when he was first elected in 2017.
But the details immediately triggered an angry response from the unions, with plans for strikes on 19 January.
Ms Borne's handling of an explosive reform was cautious, as she announced the proposals at a news conference.
She was careful to emphasise the gradual, progressive nature of the planned changes, with extra support for those on the lowest pensions.
But, as she admitted, the reform "will spark fears and questions among the French people".
A recent poll suggests 80% of the population is opposed to pushing the retirement age back to 64. Some MPs even blame Mr Macron's policy for losing his party its parliamentary majority last year.