Bossnappers struck again in France today as four executives of Caterpillar, the heavy equipment manufacturer, were detained by their employees in a protest over redundancy plans.

Nicolas Polutnik, the director of the group's factory in Grenoble, south east France, was held along with three senior managers, according to unions demanding a renegotiation with management.

A fifth executive chose to stay with them, even though unionists said he had no role in the dispute and could go.

The bossnapping in Grenoble is the third such incident in a month in France, where rising unemployment and a history of violent conflict are combining to create an inflammable context.

Benoi Nicolas, representative of the left-wing Confederation Generale du Travail union, said: "We are holding them in the director's office and we are talking with them so that they agree to open a works council meeting un unblock the negotiations.

"We're not going to let them go. They're a bit shocked".

He added" We have given them something to eat and we've given them half to hour to think about starting the negotiations.

With Caterpillar is cutting 5,000 jobs worldwide, including 733 in France, the dispute centres on redundancy payments.

Unions are demanding a minimum of €30,000 whilst Caterpillar has offered €10,000.

The two other recent bossnappings in France were also sparked by a dispute over lay-off terms. One involved Sony France, the chief executive and director of human relations were held for a day. The second concerned the French industrial director of 3M, the US conglomerate, who was detained for two days.

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