|Unions have vowed to continue to protests against pension reforms [AFP]
French unions have challenged a back-to-work order in court, a day after the country's senate voted in favour of the government's controversial pensions reforms.
Protesters showed no sign of giving up further industrial action and have vowed more days of strikes in their months-long struggle against the bill that extends the retirement age from 60 to 62.
The union's legal challenge on Saturday focuses on a "requisition" order to employees at the Grandpuits oil refinery, a key plant that supplies the Paris region with 70 per cent of its fuel, for them to return to work.
A requisition can be issued by French authorities when they believe a strike poses a threat to public order and compels strikers to return to work, under threat of prosecution.
Riot police were sent in to clear pickets blocking the site early on Friday, clearing an 80-strong "citizens' cordon" of strikers and local supporters.
Union officials said a number of the protesters were hurt when they were kicked by police.
But staff who had been ordered back to work downed tools again overnight after a judge ruled the government's requisitioning had been illegal.
The judge said the prefect, or central government's local representative, had erred by requisitioning virtually all the workers at the refinery, which meant the site was running normally.
The authorities immediately issued another requisition order at the plant, which the unions are now appealing against.
The interior ministry said that the new requisition only ordered to work a "strictly necessary" number of staff and that trucks were taking fuel from the refinery's depot.
French families faced major fuel shortages on Saturday at the start of half-term holidays, with unions blockading all 12 refineries in the country.
Six out of 10 filling stations were dry or had run out of at least one fuel in western France and a third in the Paris region, Jean-Louis Borloo, the energy minister, told journalists.
Seven of France's 100 administrative areas or departments were short of fuel after a spate of panic buying brought, he said.
Protests against the pension law have become the biggest battle of Nicolas Sarkozy's, the French president, first term.
With poll ratings rapidly declining, he has staked his credibility on a reform he says is essential to reduce France's public deficit.
Opposition groups say the reforms unjustly penalise workers for the failures of global finance and have called instead for tax rises on banks and the rich.
More than a million people took to the streets on Tuesday, the sixth day of nationwide action since early September, and this week rioters burned, smashed and looted while police fired tear gas and
arrested hundreds of demonstrators.
As well as increasing the minimum retirement age, the reforms raise from 40.5 to 41.5 the number of years an individual needs to contribute to social security funds before being eligible to collect a pension.
They will also change from 65 to 67 the age at which retirees can collect a full pension.
Despite the anticipated new law, France would still have one of the lowest minimum retirement ages in Europe.
And the broader measures Sarkozy is pushing through to cut the deficit are far milder than those seen in countries such as Britain, which unveiled $126.3bn in spending cuts this week.