Giant dummies are paraded during a workers' demonstration in Paris

Tens of thousands of workers protested across France in what experts say amounts to the biggest challenge to date facing French Prime Minister Dominique de Villepin and his four-month-old government. The strike has disrupted rail and public transportation services, and forced airline cancellations at airports.

Thousands of demonstrators gathered in the Place de la Republique, in northern Paris for the kickoff of one of many protest marches taking place across the country. The atmosphere was festive, with big colored balloons, representing various workers' unions, flying overhead.

But there was also an angry undertone to the demonstration.

"De Villepin, De Villepin" one man chanted into a loudspeaker, "you are not worth anything. You have done nothing but break things during your first 100 days in office."

The man was referring to Dominique de Villepin, who was appointed prime minister last May, after French voters rejected the referendum on the European constitution. Many analysts said the rejection amounted to a protest vote against a series of unpopular government reforms.

Mr. de Villepin's popularity has gone up in recent weeks. But that does not mean the French entirely approve of the way he is handling his new job. Many denounce the center-right government's efforts to kickstart France's ailing economy through privatization plans and a new measure making it easier to hire and fire workers. Jean-Marie Rabory, a member of France's CFDT trade union, is one of them.

Mr. Rabory said strikers here are angry about a lot of things. Besides the government's new hiring program, he says, French workers are worried about their job security and pay.

Nearby, teacher Sandrine Carvalhosa had other grievances. Ms. Carvalhosa is a 25-year-old primary school teacher who works outside Paris. She says public schools lack qualified teachers. And she says teachers are generally poorly paid.

Surveys show up to three-quarters of French support the demonstrations. Mr. de Villepin said he had "heard" the message being sent from the streets. But protesters here are waiting to see whether he will respond to it.