PARIS — French factory workers angry over layoffs and cost cuts locked up their bosses at a Michelin tire plant and a U.S.-owned cigarette-paper mill in a new eruption of "bossnappings."

The auto and auto parts industries have been particularly hard-hit by cutbacks and a backlash by French workers during the country's worst recession in decades. The new seizures of executives this week come on the heels of a string of threats by workers around France to blow up their workplaces to make themselves heard.

About 50 workers at Michelin's plant in Montceau-les-Mines in eastern France locked up four managers, including the director, on Tuesday night. The managers were released early yesterday after regional officials offered to mediate, Michelin spokeswoman Fabienne de Brebisson said.

As tensions peaked, workers caused considerable damage to an administrative building, breaking windows and damaging bathrooms, she said.

The incident comes amid tensions and negotiations over Michelin's plans, announced last month, to reduce French staff by more than 1,000.

Unions are angry over a sanction against a worker punished for refusing to use machinery on which he hadn't been trained. Patrick Duvert of the CGT union said the punishment was a sign of growing pressure by management.

While French officials have denounced such violent worker protests, police are rarely brought in and the hostage-takings usually end peacefully.

Finance Minister Christine Lagarde said she "condemned all acts of violence or situations of blackmail" by angry employees. "What works is dialogue," she said on France-2 television yesterday.

Workers at a mill that produces cigarette paper held four of their bosses during meetings Tuesday night about layoffs. The lock-up, which lasted four hours, occurred in the town hall of Malaucene in southeast France.

The mill, owned by Alpharetta, Ga.-based Schweitzer-Mauduit International Inc., is slated to shut down in September. The 211 workers are asking the government to intervene to help find a buyer for the plant, according to the CGT union.

Industry Minister Christian Estrosi met yesterday with laid-off workers from an auto parts plant in central France who placed gas canisters around their factory and threatened to blow it up if they didn't get larger severance packages.

Estrosi said more than 200 employees had already accepted a "transition package" by which the state guarantees that workers get 95 percent of their wages for the next 12 months.

But CGT union leader Guy Eyermann said yesterday's meeting wasn't enough. "We're very disappointed, this is just more promises," said Eyermann, requesting jobs for the 366 laid-off workers at the New Fabris plant.

The workers at the plant want $43,000 each from Renault SA and PSA Peugeot-Citroen, blaming French automakers for causing the collapse of their factory.

Laid-off workers at a Dutch petrochemical company that supplies the auto industry blocked production for several hours yesterday at their factory in Fos-sur-Mer on the Mediterranean coast. The 72 workers at the LyondellBasell plant want to be rehired in new jobs. They ended their protest after management agreed to a special meeting with employees.