Members of some of France's hard-left unions, including many energy workers, laid down their tools on Thursday in protest of higher prices and planned pension reforms.
Refineries, nuclear plants, some schools and some public transport have suffered disruptions as the union leading the strike, CGT, includes membership from the transport and energy sectors.
The CGT framed Thursday's strike as a possible precursor to social unrest if President Emmanuel Macron goes too far with plans to raise the retirement age from 62 to 64 or 65.
"For us this is a starting point, the start of a movement," the union's leader, Philippe Martinez, told broadcaster France 2.
The strike comes as private and public companies face increasing demands from workers to counterbalance rising prices with pay raises.
Which sectors are affected by the strike?
The Eiffel Tower in the capital, Paris, was closed to visitors on Thursday because of the strike, the operating company said.
About 20,000 people visit the city's most famous landmark on average every day.
Disruptions were expected for bus and suburban train services, as well as regional restrictions on rail traffic. The metro system in Paris itself, however, has been little affected.
In the education sector, the SNUipp-FSU union expected one in every 10 primary schools to close in the capital.
There have been major repercussions for the energy sector at a time when a record number of nuclear power plants are already out of operation, with grid output seriously reduced.
The disruption is largely due to the participation of the electricity union FNME in the 24-hour strike.
Strikes also hit TotalEnergies refineries for a third day, with walkouts at seven sites.
