Union sources said that passenger services to Britain were unaffected, but that as well as the dock workers a majority of the estimated 1,200 shipping agents had also stopped work at the country's second biggest terminal container port after Marseille.
The influential CGT union also called for protest marches in Paris and seven other French cities over lack of job security.
French unions fear that the Socialist government's efforts to plug a 37-billion-euro hole in public finances will lead to more job cuts.
CGT boss Bernard Thibault said: "We are not naive, the employers are on the offensive. There is pressure on the government to get measures that are favourable for employers and in this situation wage earners cannot remain on the sidelines."
French unemployment recently breached the three-million mark and crossed 10 percent.
Last week, after a short but extremely effective campaign by small business entrepreneurs, the government rowed back on a plan to tax the owners of small businesses up to 60 per cent when they sell their companies.