MARSEILLE, France (AP) — Protesters clashed with police in several French cities on Thursday over proposed reforms to the country's labor rules and strikers have forced cancellations and delays at two airports serving Paris.

Thousands of demonstrators marched in Paris, and violence broke out when several dozen people, many with their faces covered, started throwing objects at police. Police used tear gas to disperse protesters.

French television also showed clashes in the southern city of Marseille, and Nantes and Rennes, in western France.

An air traffic controllers strike canceled 20 percent of all flights at Paris' Orly Airport and caused delays at Charles De Gaulle, according to a notice on the Paris airport authority website Thursday.

France has seen a series of strikes and protests against the labor reform bill, which is aimed at encouraging companies to hire. Critics on the French left say the reforms will compromise France's hard-won worker protections without curbing the country's stubbornly high unemployment rate.

The bill will be debated at France's lower house of parliament next week.