More than a million people have joined a day of protests and strikes, according to France's interior ministry, against plans to push back the age of retirement from 62 to 64.
Some 80,000 protesters took to the streets of Paris, with demonstrations in 200 more French cities.
President Emmanuel Macron called the reforms "just and responsible" - but they are facing a make-or-break moment.
The strikes severely disrupted public transport and many schools were closed.
Protests took place across France, in Nantes, Lyon, Bordeaux, Marseille and Toulouse, as train drivers, public sector workers and refinery staff walked out.
The head of the big CGT union, Philippe Martinez, put the total number of protesters at beyond two million, higher than the government's 1.12 million figure. They said 400,000 peopled had joined the biggest march, from Place de la République in Paris.
Buoyed by their success, the unions called another day of action for 31 January.