Trade unions mounted huge protests across France today over plans to raise the retirement age from 60 to 62.
However, President Nicolas Sarkozy insists he is determined to implement the unpopular pension reforms.
Union leaders said 2.5m protestors took to the streets in rallies throughout the day, though the official estimate from the interior ministry was 1.1m.
French union leaders demanded the centre-right government heed their call to backtrack or run the risk of an escalation.
'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 Paris rally.
Union leaders will meet tomorrow afternoon and if they did not get a favourable response from the government another strike is possible, according to Mr Thibault.
The French strikes cut national rail services by about 50% and disrupted underground train services in Paris - but not as much as initially feared.
One in four flights at Paris airports were cancelled.
Unions said one in three high-school teachers stopped work and the post office said one in five employees stayed away.
Voters against 'unfair' plans
Opinion polls show two-thirds of voters think Mr Sarkozy's plans to raise the retirement age from 60 to 62 and make people work longer for a pension are unfair.
However two-thirds also think the strikes will make no difference.
'Never in polling history have the French people been so convinced that there's a social injustice,' said political analyst Roland Cayrol, from Paris's Sciences Po university.
The conservative government says the reform is essential to balance pension accounts by 2018, reduce the public deficit and preserve France's AAA credit rating, which helps it to service a big debt as cheaply as possible in financial markets.
The labour unrest mirrors action in other European countries against austerity measures. Governments in Greece, Spain, Italy and Romania have so far faced down strikes to impose painful pay and public spending cuts, and London's underground rail network is also paralysed by a strike today.
Ministers say the pension bill's key principles are non-negotiable.
Most major European countries have an official retirement age of 65, and some, such as Germany and Britain, plan to raise it gradually to 67 or beyond.
But the real effective retirement age in France is similar to that of its neighbours, according to the OECD.
A number of flights to and from France were affected by the strike.
Aer Lingus confirmed that one of its flights from Dublin to Paris had been cancelled.
Passengers were to be accommodated on a later flight to Paris this evening.
Ryanair said its flights to and from French airports and flights that overfly France were cancelled.
Ryanair advised passengers to check its website for further details.
