PARIS (Reuters) - French workers facing layoffs have threatened to dump a toxic substance into the River Seine if their demands for extra compensation are not met, union representatives said on Thursday.

The Palais de Justice, or Courts, is reflected in the waters of the River Seine in Paris on August 6, 2009. REUTERS/Jacky Naegelen

It is the latest in a series of threats and other headline-grabbing actions this year by French employees of companies hit by recession. In other cases, workers detained managers overnight or threatened to blow up factories.

The employees of struggling trucking company Serta, located in the Normandy village of La Vaupaliere in northwestern France, are demanding an extra 15,000 euros ($21,340) each on top of the minimum compensation package for laid-off workers.

They are threatening to dump 8,000 liters of a toxic liquid into a sewer that runs into the Seine. The threat is timed to coincide with a court hearing on Thursday that could result in the company being sold or closed down.

“It’s a monstrous waste and the employees mean to make those responsible pay,” Jean-Pierre Villemin, a staff representative from the CFDT labor union, told Reuters by telephone.

Before it ran into difficulties, Serta employed about 240 people. Some 80 jobs have already been cut in a first round of layoffs. Villemin said two bidders had offered to buy Serta, but the workers expect further layoffs even if the firm is sold.

He said the workers did not wish to carry out their threat and had made it mainly to draw media attention to their plight.

Similar tactics have been used by workers at companies in several other parts of France, with mixed results.

“Bossnappings,” the temporary detentions of managers on company premises, and threats to blow up equipment or plants, have given workers exposure in the national media and sometimes prompted ministers and other authorities to wade into disputes.

Such shock tactics have sometimes, but not always, resulted in improved compensation packages for laid-off workers.