* Factory manager blockaded in factory
* Workers demand better lay-off terms
* Economic crisis raises social tension in France
* French unemployment rising, new data show
(Adds new quotes, unemployment figures)
By Clotaire Achi
PITHIVIERS, France, March 25 (Reuters) - Workers at a factory operated by the U.S. firm 3M looked set to hold their French manager hostage for a second night in protest against plans to lay off half the staff.
The industrial director of the group, Luc Rousselet, was barricaded in an office on Tuesday evening and workers have refused to let him out until he agrees to more favourable terms for the 110 employees who face the axe.
"These people have more to complain about than me and I knew there was this risk when I came here," Rousselet told reporters from his office, where the door has been blocked by a wardrobe.
Unions said no agreement had been reached.
"The director says it is impossible for him to negotiate," said Jean-Francois Caparros of the Force Ouvriere union.
Locking up managers is becoming a tradition in French labour disputes, with police unwilling to intervene to avoid violence.
Earlier this month employees at a Sony factory in southwest France detained the chief executive and human resources director of the Japanese group's French arm overnight and eventually secured better terms for workers facing dismissal.
Unions at the 3M plant in Pithiviers, near Orleans, south of Paris, are demanding more money for departing staff, guarantees for those remaining and payment of salaries for those who went on strike over the redundancy plan.
"Until we have a commitment from 3M that they will increase pay packets and are ready to discuss our conditions for negotiations, then Mr Rousselet will have to remain here," Caparros told Reuters.
"If he wants to involve the police, then he will have to send for them, but it is out of the question that he leaves without discussing our conditions," he added.
Diversified technology group 3M makes everything from scotch tape to optical films for liquid crystal displays. France is its sixth largest market and it employs 2,800 staff here at eight sites, according to the group's website.
"I am among the 110 people laid off and I know that I will not find another job in Pithiviers," said Edwige Ferrage, who had worked at the company for 38 years.
"I would never have imagined finishing my 3M career like that. It hurts. I feel humiliated, like all the workers here."
The company has said it needs to cut jobs at Pithiviers to reduce overcapacity because of falling demand.
"We have had five rounds of negotiations ... and at the end of the last one we reached an agreement on a certain number of points, but there are still measures left where there are substantial points of disagreement," Rousselet said.
Social tensions are rising in France because of the economic crisis. More than two million people are already unemployed and hundreds of thousands more are expected to lose their jobs this year as the recession deepens.
Unemployment jumped by 79,900 in February, a 19.0 percent rise on the year, new figures showed on Wednesday.
Between 1.2 and 3 million people took to the streets of French cities last week to denounce the government's handling of the crisis and workers from a Continental tyre factory facing closure took to the streets of Paris on Wednesday to protest. (Additional reporting by Mourad Guichard in Orleans; writing by Crispian Balmer and Anna Willard; editing by Tim Pearce)