(Adds union comment)

PARIS (AFP)--French Prime Minister Francois Fillon called Wednesday for charges against laid-off workers who vented their anger by trashing a government building as fears grew of labor unrest turning violent.

Workers from a plant owned by German tyre company Continental AG (CON.XE) ransacked the offices Tuesday in the latest flare-up of labor anger that has also seen employees take managers captive at factories hit by the economic crisis.

"These are violent acts that are unacceptable," Fillon said after Continental workers smashed windows and wrecked computers at the offices of the regional administration in Compiegne, northeast of Paris.

Fillon said they should face legal action for the rampage triggered by a court's refusal to block the company's decision to shut down the factory and scrap 1,120 jobs.

"But at the same time, these are violent acts carried out by a minority of workers and they should not be the focus of all of our attention, which should instead be directed at the future of Continental," he told France Inter radio.

Continental announced the closure of its factory in Clairoix, north of Paris, in March, the biggest single closure announced so far in France, and workers have been waging a vocal campaign to save their jobs.

Xavier Mathieu, the CGT union leader at the plant, hit back at the government on Wednesday, insisting workers were driven to desperation by a brutal management strategy.

"The people you saw yesterday were not vandals, but simply people who are angry, outraged, on the verge of nervous breakdown."

"They are talking about broken windows, computers, that's nothing compared to the 1,100 lives that are about to be shattered," he said, urging the state to impose a three-month moratorium on the plant closure.

But the action at Continental and the wave of "boss-nappings" have raised alarm over spiraling social unrest in France, which looks set to sink deeper into recession in the coming months.

Fillon said the economy would shrink by 2.5% in 2009, revising the government's previous forecast of a 1.5 percent fall, which was viewed by independent economists as optimistic.

The International Monetary Fund for its part forecast a decline of 3.0 in France's gross national product in a report issued Wednesday.

Facing strong public resentment over corporate perks, Fillon also took aim at executive bonuses, charging that companies were stoking tension with "shocking" payouts to their managers.

The former boss of rescued Franco-Belgian bank Dexia, Axel Miller, walked away from his job with a EUR825,000 severance package, according to the bank's annual report released on Monday.

In the latest "boss-napping" incident, workers at a US-owned Molex Inc. ( MOLX) car parts supplier in southern France held two managers captive at the plant for more than 24 hours before releasing them late Tuesday.

President Nicolas Sarkozy earlier this month said locking up company bosses in their offices was illegal and that he would not allow "matters to go on like that."

No charges have so far been brought against employees for detaining their bosses. In each case, the managers were released unharmed, and most of them agreed to new negotiations.