Battle between Sarkozy and unions over pensions enters crucial phase with workers and students expected to take to the streets

The battle between President Nicolas Sarkozy and the French unions over pension reforms enters a crucial phase today with a new wave of strikes and protests across the country.

Workers and students are expected to take to the streets in an escalation of industrial action against government plans to raise the official retirement age to 62, with walkouts bringing disruption to France's transport network, schools and oil refineries.

For the first time, several unions have voted for open-ended "rolling strikes" aimed at forcing concessions from the president, who has made pension reform the centrepiece of his five-year term in office.

The announcement that secondary school and college pupils will join the demonstrations against Sarkozy, whose popularity is at a record low, raises the spectre of May 1968, when a series of student strikes led to rioting and nearly brought down the government.

Today's strikes are expected to force the cancellation of up to half of flights in and out of France as well as two out of three TGV high-speed trains. There are warnings of severe disruption to other transport and public services, though the Eurostar will not be affected. French ports, where workers have been striking against separate reforms, will be badly hit and there are warnings that strikes at oil refineries could lead to petrol shortages.

Most strikers are expected back at work on Wednesday, but some unions have threatened to call on members to vote each day whether to continue the strike indefinitely. Sarkozy's office says he will not back down on measures he believes will help his re-election for a second term in 2012. Some French analysts have warned the clash could spark serious unrest. In Le Parisien newspaper the former Socialist prime minister Michel Rocard spoke of a "danger to the country". Jean-Claude Mailly, of the Force Ouvrière (Workers' Force) union, told French radio: "We're forcing a wall. Only a show of force, a big protest, can force the government to move."

Ministers have warned union leaders not to use students to inflame the conflict.

Raymond Soubie, an advisor to Sarkozy, has described the call to students to strike as "irresponsible" but Socialist spokesman Benoit Hamon blamed the government for hardening attitudes.

"Intensifying the action might force the government to finally realise that the reform is unfair and inefficient," he told Le Parisien.

Last night the Sénat, the upper house of the French parliament, was rushing through a vote on the second pillar of the reform that would raise the age at which workers can retire with a full pension from 65 to 67 by 2018.

The Sénat passed the proposal increasing the minimum retirement age last week. The whole pension bill is expected to get full parliamentary approval by the end of the month. It will then go to the constitutional council for final approval.