French public sector workers are holding a day-long, nationwide strike to protest against the government's social and economic policies.
Tens of thousands of people rallied in Paris and other cities.
Transport, schools and other services were disrupted by the strike, which was supported by all the major unions.
The protest comes two days after regional elections in which President Nicolas Sarkozy's centre-right UMP party suffered a heavy defeat.
Resistance to Mr Sarkozy's economic reform programme was widely thought to have contributed to the loss.
On Monday, the French president reacted by reshuffling his cabinet, replacing Labour Minister Xavier Darcos with Budget Minister Eric Woerth.
Mr Sarkozy has also suggested he may slow the pace of unpopular reforms.
Train workers went on strike over planned reforms to the pension service, prompting travel problems across the country's rail network.
About half the trains were running on Paris commuter lines on Tuesday morning, while nearly two-thirds of national high-speed TGV services were operating, according to French news agency AFP.
National rail operator SNCF said services would be disrupted until early on Wednesday.
Teachers protesting over job cuts also joined the demonstration, along with other public sector workers complaining about working conditions and their lack of spending power.
No disruption was expected on the international Eurostar and Thalys rail links.