Faces lit by flames from burning tyre barricades, a handful of bitter trade unionists resign themselves to obeying a government order to get back to work at the Grandpuits oil refinery near Paris.

Paramilitary police have just broken up their picket at the vital refinery using their bare hands, nevertheless injuring three workers, unions said, as nationwide fuel shortages caused by pension reform protests bite.

Without batons, tear gas or helmets, police moved in the early morning, clearing an 80-strong "citizens' cordon" of strikers and local supporters to forge a path into the plant during a skirmish that lasted a few minutes.

"The police charged to clear the citizens cordon and unfortunately we have two people with throat injuries and another with foot injuries," said CFDT union delegate Mohamed Touis as the acrid smoke from burning tyres clears.

"They arrived in force and hit out violently. If anyone was acting like thugs, it wasn't the strikers," said Julien Calmettes, a railworker and trade unionist who had come to join the picket.

Workers at the plant have now been served with legal notices requiring them to get back to work or face possible jail terms.

The order, known in France as a "requisition", can be issued by authorities when they believe a strike poses a threat to public order. But the unions do not agree public order is at stake and want to challenge the move in court.

One plant worker, wearing a black jacket with "Requisitioned" scrawled on the back, obeys the edict to get back to work and walks into the refinery: "I've been requisitioned, but it stinks."

But the head of the powerful CGT union, Bernard Thibault criticised the government for "purely and simply preventing the right to strike as guaranteed by the constitution" after police took control of Grandpuits.

CGT representative Charles Foulard said: "For now, police have taken over the factory, the requisition is in effect, so we're going to meet with the organisations, and debate with the workers to see how we're going to continue the struggle."

Foulard later slammed "raids on those exercising their right to strike", drawing a parallel with the World War II pro-Nazi regime of Philippe Petain.

"In our country's history we have gone through moments of Petain. Today, there are raids on our social gains, raids on our pensions, raids on the right to strike," he said.

Workers here, as elsewhere in France, blame the government for its tough stance and refusal to negotiate.

"As long as there's no mediator, such as the industry ministry, we can't see how this is going to end, seeing as how there's 12 refineries shut down," said Mohamed Touis.

All 12 of France's oil refineries have been hit by industrial action against President Nicolas Sarkozy's unpopular plan to raise minimum retirement from 60 to 62 in recent weeks.

It is not even known when the Grandpuits refinery will stop operating once more. For now, the authorities are happy to be able to fill up some fuel tanker trucks.

"They're going to fill the trucks? And then what, when the depot's stocks are finished?" says a CGT union member who asked not to be named, clad in an orange jacket and baseball cap.

Shortly before midday, around 10 people enter the refinery carrying bread and other food, bringing that they call "the bread of struggle" to the strikers.