Twenty police officers and six civilians were injured Tuesday as protests in Paris over a labor reform bill turned violent.
Authorities in the French capital said they detained about 21 people engaged in violent clashes between police and masked protesters.
Riot police responded with tear gas and water cannon to disperse the crowd of several hundred demonstrators.
In a separate protest, Air France pilots were striking to demand better working conditions. The company said it canceled about 20 percent of domestic and international flights.
Weeks of strikes and demonstrations have been part of a nationwide labor union action in response to a bill that would allow employers more freedom to lay off workers and extend working hours.
President Francois Hollande's socialist government hopes the bill will energize hiring and the economy, but unions consider it a threat to fundamental workers' rights.
The clashes erupted as international attention is focused on France as the host of the Euro 2016 football championships, which have also been marred by violence among fans.