(Adds details, background)
By Valerie Parent
PARIS Feb 6 (Reuters) - A 24-hour strike disrupted France's ports on Thursday, including tanker traffic at its main oil hub of Fos-Lavera on the Mediterranean coast, while the impact on the French power sector was limited.
Thursday's nationwide action was called by the CGT union to protest a 2008 port reform that transferred some port workers from the public sector to the private sector.
It was well supported by dockers and brought most ports to a standstill, Tony Hautbois head of the CGT's port section said.
"All in all 85 to 90 percent of activity has been blocked today in France," he said.
At Fos-Lavera near Marseille, the strike was holding up six vessels inside the port, including one crude tanker and five refined products tankers, and another three refined products tankers outside the port, a port spokeswoman said.
Ship activity continued as normal to the liquefied natural gas terminal and the LyondellBasell petrochemical plant at the Fos-Lavera hub, she added.
At Le Havre on the north coast, France's largest container port and also an oil terminal, some ship arrivals had been rescheduled to avoid the strike, said Herve Cornede, commercial director at Haropa, port operator at Le Havre, Rouen and Paris.
Oil products traders said, however, that the strike was having a limited impact on the products market, because they expected disruptions to cargoes to be short-lived.
The CGT has also called for a further one-day strike at French ports on Feb. 12 to protest grievances about the port reform.
"With the port reform we were promised better days, more traffic and new jobs," Hautbois said. "In reality, our jobs and our working conditions are being called into question."
Freight and fuel companies have welcomed the reorganisation of French ports under the previous conservative government and said it has been improving port performance.
"We have had far fewer incidents and supply disruptions, things that you would have seen in the past, so at this stage it's a rather positive factor for our business," Jean-Louis Schilansky, head of oil-sector lobby UFIP, said on Tuesday.
Thursday's anti-austerity protests had little impact on power production. EDF's nuclear power fleet was unaffected, and only 350 megawatts of thermal power capacity were offline, the equivalent of a third of a nuclear reactor.
But the CGT is calling for power and gas workers to launch a two-week strike from Friday to voice specific grievances such as underinvestment in thermal power, the union said.
The call does not apply to refinery workers who fall under another branch of the CGT. (With additional reporting by Lin Noueihed in London; Writing by Gus Trompiz; editing by Michel Rose and Jane Baird)