France's government is facing massive hostility to measures that would give bosses more flexibility in hiring and firing, in a bid to turn around a record 10.2 percent unemployment rate.
An online petition against the El Khomri draft law, named after Labour Minister Myriam El Khomri, has attracted more than a million signatures while a poll showed seven in 10 people were opposed to the proposed changes.
President François Hollande, who campaigned on a promise to improve the prospects of young people, said on the eve of the protests that he wanted to help them "have more job stability".
"We must also give companies the opportunity to recruit more, to give job security to young people throughout their lives, and to provide flexibility for companies."
Outspoken Economy Minister Emmanuel Macron said in an interview with France Inter radio on Tuesday that unemployment had not dropped below seven percent in 30 years.
"Have we tried everything? Let us look outside France. What has happened elsewhere? They have all evolved, they have all done things," he said.
Currently French employers are loath to take on permanent workers because of obstacles which prevent them laying them off in lean times.
Young people leaving university find themselves working on temporary contracts for years at a time or doing internship after internship while hoping to secure a job.
The reform would also cut overtime pay for work beyond 35 hours - the working week introduced in 2000 by Socialists Martine Aubry and Lionel Jospin.
The French Cabinet is now to examine the draft law on 24 March.
1 train in 3 in the Ile de France region for the Transilien regional rail service.
1 TGV in 2 - East of France
1 TGV in 3 - North, Atlantic coast and South-East
Ouigo : 4 trains in 10
80% of Eurostar, 100% of Thalys.
Bus, trams and metros are not affected by the strike except the RER B with only 2 trains in 3 and RER D with 1 train in 3.
No trains running between Châtelet-les-Halles and Gare de Lyon.
07:20, le trafic est perturbé entre Gare du Nord et Aeroport CdG 2 / Mitry - Claye (mouvement social) #RERB— RER B (@RERB) 9 Mars 2016