Public sector workers demonstrate over pension reforms in Marseille, southern France, May 22, 2008. French unions staged nationwide protests on Thursday against plans by President Nicolas Sarkozy to make people work longer to qualify for a full pension. [Agencies]

Factory workers and dockers angry at privatization plans joined the marches in several cities including Marseille.

Walkouts were reported across the French public sector, with between 10 and 20 percent of postal, utilities and telecoms employees joining the strike, officials said.

And morning radio slots were replaced by music on public stations France Inter and Radio France Internationale.

France's five main unions are leading protests against plans to increase the number of years worked to draw a full pension, from 40 to 41, starting next year.

Written into a reform passed in 2003, the pension changes continue to raise hackles in union ranks.

"There are other financial solutions aside from asking workers to stay at work longer," said Bernard Thibault, head of France's biggest union, the CGT. "The government is going to have to change its line under pressure."

The head of the CFDT union, Francois Chereque, has accepted the reform in principle but says it should take into account the physical strain -- and the knock-on effect on life expectancy -- of various lines of work.

But Sarkozy's right wing government has vowed to stand firm.

"The question was settled in 2003," Prime Minister Francois Fillon said on France 2 television Wednesday night.