A spate of bossnappings by French workers has put President Nicolas Sarkozy in a tight spot, caught between the need to enforce the law and the risk of exacerbating unrest during the economic downturn.

Managers have been held hostage at factories for up to 24 hours by staff angry about layoff plans in four separate incidents since March 12. In a variant, a billionaire boss was blocked in his taxi by employees for an hour on March 31.

What's this about holding people captive? We have the rule of law in this country. I will not let such things happen, Sarkozy told a group of entrepreneurs on Tuesday.

The same day, workers at a British-owned plant detained four managers, including three Britons, and held them overnight. As in the three previous bossnappings, police did not intervene. Staff let the managers go on Wednesday after promises of talks.

Apart from the humiliation of seeing his warning ignored, Sarkozy now faces a dilemma in how to handle similar incidents.

Employers' groups and politicians from his own center-right camp say such acts are unacceptable.

However difficult the situations faced by employees, it is not acceptable to break the law, three bosses' groups said in a joint statement this week.

But labor unions and the left-wing opposition say workers facing layoffs in a context of recession and booming unemployment are desperate, so these acts are understandable.

I'm against violence but if these things keep happening it's because there is an underlying despair, said Socialist legislator Jean-Marc Ayrault on Canal+ television on Thursday.

PUBLIC OPINION SPLIT

Public opinion is split. A poll released on Tuesday found that 50 percent of people surveyed objected to bossnappings while 45 percent said they were acceptable.

Sarkozy's own ratings have tumbled during the downturn and he is particularly unpopular among blue-collar workers.

His Tuesday comments against bossnappings angered workers at a plant run by U.S. company Caterpillar who detained their managers on March 31. Sarkozy had promised to save them and invited them to meet him, but they rejected the invitation.

I don't see why we should go and see him just so he can politely insult us, since he seems to think we are delinquents for having detained management for a few hours, said Alain Debain, one of the Caterpillar workers, on i-Tele on Thursday.

The risk of sending in the riot police when the next hostage-taking occurs is that, far from discouraging such acts, it could cause them to proliferate.

Turning a blind eye carries risks as well. All four plants where bossnappings have occurred are foreign-owned, and the head of the CGPME employers' group, which represents small and medium businesses, said foreign investors could be put off France.

Maybe companies that have their headquarters abroad will decide to stop investing in our country and that would not be to the advantage of France or of our workers, CGPME head Jean-Francois Roubaud told i-Tele.

Around 22,000 foreign companies employ more than 2 million people in France, according to the Invest in France agency.

(Editing by Jon Boyle)