French riot police have used water cannons and tear gas after demonstrations against a new government plan to reduce job protection turned violent.
Protesters claimed 1.5 million marched across the country against the government's First Employment Contract (CPE).
The measure will allow employers to end job contracts for under-26s at any time during a two-year trial period without having to offer an explanation or give any prior warning.
The protests were the biggest show yet of escalating anger that is testing the strength of the conservative government before elections next year.
At the close of a march in Paris that drew a crowd of tens of thousands, seven officers and 17 protesters were injured during two melees, at the Place de la Nation in eastern Paris and the Sorbonne University. Police said they arrested 156 people in the French capital.
Four cars were set alight, police said, and a McDonald's restaurant was attacked along with store fronts at the close of the march.
Tensions escalated later as about 500 youths moved on to the Sorbonne, trying to break through tall metal blockades erected after police stormed the Paris landmark a week ago to dislodge occupying students. The university has become a symbol of the protest.
Police turned water cannons on the protesters at the Sorbonne and were seen throwing youths to the ground, hitting them and dragging them into vans.
Protest organizers have urged President Jacques Chirac to prevent the law from taking effect as expected in April.
The group issued an ultimatum, saying it expects an answer by Monday, when leaders will decide whether to continue protests that have paralyzed at least 16 universities and dominated political discourse for weeks.
"We give them two days to see if they understand the message we've sent," said Rene Jouan of CFDT, France's largest union.
Youth joblessness stands at 23 percent nationwide, and 50 percent among impoverished young people. The lack of work was blamed in part for the riots that shook France's depressed suburbs during the fall.
Widespread discontent with the government has crystalized around a new type of job contract that Villepin says will alleviate France's sky-high youth unemployment by getting companies to risk hiring young workers.
Critics say the contract abolishes labor protections crucial to the social fabric.
Chirac has pushed Villepin to act "as quickly as possible" to defuse the crisis, but has backed the contested measure.
On Friday night, a group of university presidents met with Villepin and called on him to withdraw the jobs plan for six months to allow for debate.
Failure to resolve the crisis could sorely compromise Villepin, who is believed to be Chirac's choice as his party's candidate in next year's presidential election