More than one million French workers have taken to the streets to protest against austerity measures planned by President Nicolas Sarkozy's government.
The rallies came as a 24-hour national strike disrupted flight and rail services, and closed schools.
Activists are angry at government plans to overhaul pensions and raise the retirement age from 60 to 62.
Union leaders say more strikes and protests are possible if the government fails to give an adequate response.
"If they don't respond and they don't pay heed, there'll be a follow up, and nothing is ruled out at this stage," Bernard Thibault, leader of the large CGT union, told a rally in Paris.
France's retirement age is lower than many countries in Europe, but analysts say the issue is polarising politics in the country.
Labour Minister Eric Woerth introduced the pensions bill to the National Assembly, warning of dire consequences if it did not pass.
"If we don't modify our pension plan, then tomorrow there will be no money left to pay the French pensions," he told parliamentarians.
Under current rules, both men and women in France can retire at 60, providing they have paid social security contributions for 40.5 years - although they are not entitled to a full pension until they are 65.
The government says it will save 70bn euros (£58bn) by raising the retirement age to 62 by 2018, the qualification to 41.5 years, and the pension age to 67.
President Nicolas Sarkozy says reforms are needed to cope with an ageing population and the country's budget deficit.
The government is also looking to find 100bn euros of savings in three years, and is planning cuts in the civil sector.
Some secondary-school teachers went on strike on Monday, protesting against plans to cut 7,000 jobs in education.
State railway operator SNCF said fewer than half of its TGV high-speed services were running, and there was a greatly reduced service on many other lines.
Eurostar said its trains between France and London would operate normally.
Some air-traffic controllers walked out, forcing the cancellation or delay of about a quarter of flights from Paris airports.
Air France said it was operating all of its long-haul flights as planned, but short and medium-haul flights had been affected.
Amid the disruption caused by strikes, the Interior Ministry said 1.1 million people had joined Tuesday's protests but unions claimed the figure was more than double official estimates.
The figures make Tuesday's protest bigger than a previous one in June, where more than 800,000 people took part.
Huge crowds braved stormy weather across southern parts of France, while demonstrators in Paris and the north enjoyed autumn sunshine.
In Paris, protesters shouted through loud-hailers: "Slave-driving? No, no, no. Working more? No, no, no. Fair reforms? Yes, yes, yes."
Protester Michel Prouvier told AFP news agency: "We're going to have old people living in the street."
Activists were also keen to maker a wider point, angry at the recent deportation of about 1,000 Roma (Gypsies) and a host of proposed laws which they say unfairly target immigrants and minorities.
"Pensions are a pretext for protesting against the Sarkozy system," said Adji Ahoudian, a Socialist Party activist.
Among those concerns is a proposal banning the full face veil worn by Muslim women, which was passed by the lower house in July but is now up for debate in the Senate.
Senators are also expected to debate a controversial new security law which would see recent immigrants stripped of French citizenship if they committed serious crimes such as killing a police officer.
The law would also allow electronic tagging for foreign criminals facing deportation.