Vandals have smashed doors and windows at the headquarters of the French union that has been leading months of protests against a government bill weakening French worker protections.

Paris police and the Interior Ministry said the damage to the CGT headquarters was inflicted Saturday in the Paris suburb of Montreuil, and promised to investigate.

CGT chief Philippe Martinez, the public face of the months-long protests, visited the site Saturday to denounce the damage.

Offices of a more moderate union, CFDT, were also damaged in recent days and the governing Socialist Party's offices have been vandalized around the country.

Critics accuse Socialist President Francois Hollande of betraying his leftist base with the labor bill, designed to boost hiring by giving employers more flexibility to hire and fire and extend working hours.