Workers at a plant owned by Michelin detained four managers on July 21, the company said, preventing them from leaving a factory in another case of "boss-napping."
Workers at the Michelin plant in Montceau-les-Mines in the central region of Saone-et-Loire were protesting against the treatment of an employee on a short-term contract.
"Four members of the management, including the director of our Monceau factory, are being held by a group of about 50 workers," a spokesman for the group said.
The employee at the centre of the dispute was laid off for two days after "refusing to work," the spokeswoman said. Union official Patrick Duvert said he was not trained to operate machines and had refused to put himself at risk.
The managers had access to their offices and were able to make telephone calls but were being prevented from leaving the factory, the spokeswoman said.
Union representatives at a string of French companies have recently barricaded their managers in their offices during negotiations over job losses and restructuring, releasing them only when concessions have been agreed.
The wave of incidents, which in some cases has seen managers locked in overnight but always released unharmed, has added a more menacing twist to France's often-tense industrial relations.
Copyright Agence France-Presse, 2009