Police moved in at dawn, using a fire-engine ladder to get through the roof of a public hall in the western city of Rennes and flush out the protesters, some of whom had taken refuge on the roof itself.
After sometimes violent marches and 82 arrests Thursday, the head of the ruling Socialist Party condemned rampagers who ransacked party offices and daubed them with anti-government graffiti.
The protesters' anger is at government plans to make hiring and firing easier, in a flagship reform of French president Francois Hollande, plagued by rock-bottom popularity ratings ahead of a May 2017 election.
There are calls for broader street protests next week and strikes by railway workers, dockers, truckers and airport and refinery workers.
"The government has public opinion against it, a majority of the labor unions against it and the youth movement against it," CGT union leader Philippe Martinez said.
Other CGT representatives called for rolling strikes from next Monday night, arguing that the labor law change could prompt employers to cut overtime pay, Reuters reported.
Polls show as many as three in four people oppose the reform, which would allow employers to bypass national or sectorial obligations on pay and conditions by opting for in-house deals.
The last time France faced large-scale street protests was in 2011, when unions sought, but ultimately failed, to force then President Nicolas Sarkozy to withdraw a law obliging people to work longer for a pension.
Thursday's street marches mobilized tens of thousands of people, in comparison with hundreds of thousands in 2011.