Brief Four managers at a Caterpillar Inc plant in Grenoble are being held hostage by workers, AFP reports.

The agency cites an "unidentified union official" as the source of the latest French managment imprisonment news.

Earlier this month, workers at a Sony plant in Pontonx-sur-l'Adour, south-west France, held the company's local chief exec in protest at redundancy packages offered to 300 dismissed staff.

Last week, 3M workers in Pithiviers, near Orleans, mounted a similar action, barricading the group's industrial director in an office - a drastic move provoked by plans to lay off 110 employees.

In both cases, the captives were released once unions had been promised a return to the negotiating table. ®