(FORTUNE Magazine) - Anyone have a case of deja vu? Just last November, French youth torched tens of thousands of cars in a rage against a government that has presided over a 20% youth unemployment rate for years. Now they're at it again, hurling chunks of concrete at riot police on the Boulevard Saint Michel from behind burning barricades, then racing to escape the plumes of tear gas.

But something more serious than a rerun is afoot: a class war over France's future. The jobless young who sparked last November's mayhem - children of Arab and African immigrants living in Paris's grim banlieues, or suburbs - battled the same police as the students now wiping tear gas from their designer eyeglasses.

But that's it for fraternité. This time, the youth are railing against Prime Minister Dominique de Villepin's attempt to crack open the job market to their poor contemporaries in the housing projects - where unemployment for those in their 20s hovers around 40% - before the country faces another explosion of violence. Without consulting student organizations or labor unions, de Villepin pushed a law through Parliament allowing companies to fire employees under 26 without cause within two years of hiring them.

In theory that should ease companies' dread of hiring, since employees are currently all but impossible to fire. But even that modest step has ignited students like Alice Desarmot, a 21-year-old Sorbonne theater student, who faces slim prospects when she graduates next year.

"The government says they want to help the kids in the banlieues, but they're just legalizing insecurity," she says, wearing a blue sailor's cap in Paris's Place de la Republique in late March at the end of a daylong strike. Besides, she says, she feels no affinity with the jobless in the poor suburbs: "We students have never even been to the banlieues."

The divide has been festering for years, say economists and business executives.

"The students don't care about the banlieues, and the banlieues don't care about the students," says Alexandre Zapolsky, the 29-year-old CEO of Linagora, an open-source software company in Paris. Zapolsky, who launched his business at 22 and had $4 million in revenue last year, says he is hardly typical of French twentysomethings; indeed, he has watched in horror as his contemporaries battle police. "These kids are 25. They should be taking risks, not worrying about their security," he says. "France is ill. Malade."

But unions and students who believe their degrees will eventually land them jobs are willing to endure high unemployment rates, even if it shuts others out, sensing that France's generous benefits might be too expensive to share more broadly. Jobs, when found, bring up to eight weeks' paid leave, 35-hour workweeks, and a ticket to a comfortable state-funded retirement.

"Once you have a job, life is wonderful, and no one can fire you," says Radu Vranceanu, an economics professor at ESSEC, a graduate business school near Paris. "Naturally people prefer the status quo."

That's quite a reversal from the 1968 Sorbonne revolt that the parents of many of today's protesters lived through: These students are rioting to keep the system in place, not to overturn it. As violence erupted, a French newspaper, Le Figaro, published the results of a survey done last year by the U.S. polling company GlobalScan, showing that 50% of French people rejected free-market economic policies - more than twice as high as in China.

President Jacques Chirac intervened after the one-day strike and cut the firing period to one year. But further confrontations could lie ahead. Residents of the poor suburbs of Paris say more violence is inevitable there, since little has changed since last year's protests.

"It's obvious that the violence is going to start again," says Mohamed Hamidi, a high school economics teacher in Bobigny, an immigrant district north of Paris. Executives are equally convinced that France's system cannot last. They have watched as Spain and Germany have cut unemployment rates by relaxing labor laws and luring talent from abroad, and as London has become Europe's economic powerhouse, 20 years after labor violence wracked Britain.

"We still have not had our revolution," says Zapolsky, the software executive. "We need a Margaret Thatcher." Until then, Desarmot and her friends say they are ready to keep protesting in the streets, despite the tear gas and lines of riot police.