paragraph: Paris, France (CNN) -- Hundreds of French workers, angry about proposed layoffs at a Caterpillar factory, were holding executives of the company hostage Tuesday, a spokesman for the workers said. Caterpillar's French staff say they are angry about a lack of negotiations over layoffs. It is at least the third time this month that French workers threatened with cutbacks have blockaded managers in their offices to demand negotiations. Executives were released unharmed in both previous situations. The latest incident started Tuesday morning at the office of the construction equipment company in the southeastern city of Grenoble. The workers were angry that Caterpillar had proposed cutting more than 700 jobs and would not negotiate, said Nicolas Benoit, a spokesman for the workers' union. They did not want to harm the Caterpillar executives, Benoit told CNN. One hostage was released Tuesday evening leaving workers with four captives inside the Caterpillar building. The released man was a human resources director identified only as Mr. Petit, because he has heart problems, union representative Bernard Patrick told CNN. Petit had a heart attack a few weeks ago, Patrick said. The four others still being held are Nicolas Polutnik, the head of operations; two other executives; and Petit's personal assistant, he said. About 500 employees were also outside the building protesting. 
question: How many times have French workers blockaded managers in their offices to demand negotiations over proposed layoffs?
answer: Three times so far this year