Trade union and student leaders protesting in France gave the government 48 hours to comply with their demands to scrap a new law they fear will erode job security.
Issuing their ultimatum, the leaders said they might decide on a one-day general strike unless the government withdrew the law by tomorrow evening.
President Jacques Chirac and Prime Minister Dominique de Villepin would "bear full responsibility for social tensions that might follow" if they failed to meet the deadline, the leaders said.
Protesters took to the streets of France to demonstrate against the law. The marches were mostly peaceful, but dozens of youths pelted police with missiles, set a car ablaze and smashed a shop window at the end of the main protest in Paris. Police cleared them from Nation square with many rounds of tear gas.
Scattered violence was also reported in Marseille, Rennes and Lille, where police also charged and teargassed crowds.
"This is an ultimatum," Rene Valadon, confederal secretary of the Force Ouvriere union, said after union and student leaders met following the third nationwide protest in six weeks. "The government and the president have 48 hours to decide."
Organisers estimated the turnout nationwide at 1.3 to 1.4 million, with up to 400,000 of them in Paris. The official count was lower - the Interior Ministry reported 503,000 nationwide, with 80,000 in Paris.
In the government's first reaction, spokesman Jean-Francois Cope said: "Beyond the passions of the moment, don't we all have an interest in a dialogue?" He ducked a television interviewer's question whether the government would withdraw the law.
Villepin launched the new contract to spur wary employers to take on new staff, but critics decry it as a "Kleenex contract" that lets young workers be "thrown away like a paper tissue."
In the Paris unrest, 12 protesters were injured and 59 detained, police said, while four policemen were also hurt.
In Rennes, police had to storm a group of protesters to remove them from a railway line they were blocking. Another group attacked an office of Chirac's governing UMP party.