|Sarkozy's pension reform has triggered a showdown with unions that sunk a previous effort 15 years ago
Mass protests across France against plans to raise the retirement age were even larger than demonstrations held earlier this month, according to figures from both the government and a labour union.
The CFDT union said 3.5 million people had joined the demonstrations on Tuesday, while the interior ministry said 1.23 million demonstrators had turned out.
The protests took place as French trade unions staged their third 24-hour strike in a month.
Up to half the flights at Orly Airport and one-third of flights from Charles de Gaulle-Roissy in Paris were cancelled, although airlines had already rebooked many passengers ahead of the strike.
Walkouts also took place at hundreds of high schools, with teachers and students taking part in the action.
Some unions are threatening to continue the strike action beyond the usual 24-hour period, meaning the walkout could last weeks.
The protesters are seeking to force Nicolas Sarkozy, the French president, to scrap plans to raise the minimum retirement age to 62 from 60.
The French senate backed the measure on Monday as part of a deeply unpopular pension reform bill.
'Risk of radicalisation'
Jacky Rowland, Al Jazeera's reporter in the southern port city of Marseille, said workers were determined to make the government change its mind.
"French workers have campaigned long and hard for their rights and benefits, and they won't give them up without a fight," she said.
"They do remember that in the past - in 1995 and in 2006 - protest movements like this did force governments to back down on this kind of legislation.
"But it's by no means clear that it is going to happen this time around."
Three prior protests attracted crowds numbering in the hundreds of thousands but have not halted Sarkozy's pension reform plan.
"The government is taking the risk of a radicalisation of the movement," Francois Chereque, the head of the powerful CFDT union, said.
Sarkozy faces re-election in 2012 and his opinion poll ratings are at all-time lows.
David Assouline, an opposition leader, accused the president of trying to provoke a "showdown" and bring unions "to their knees".
Monday's vote, which came in at a narrow 174 to 159, shut the door on the most controversial aspect of the reform package, which Sarkozy's administration hopes to pass by the end of the month.
The senate also voted to raise the minimum age to receive a full state pension from 65 to 67.
Oil industry strike
Workers in the oil industry have also joined in the strike.
Employees at France's biggest oil port, Fos-Lavera, have now halted work for 15 straight days.
One poll of around 1,000 people published in the newspaper Le Parisien found that 69 per cent of respondents supported the new strike, while 61 per cent supported a "continuous and lasting" one.
Like other European governments looking at austerity measures, France faces a deficit and a need to improve its finances if it hopes to retain a AAA credit rating, enabling the country to borrow money at a lower interest rate.
The reform bill has already been approved in its entirety by the lower house of France's parliament, the national assembly.
The senate is now voting on it piece by piece.