CGT members at 19 nuclear power plants voted Wednesday to join the strike which has paralyzed French businesses and disrupted fuel supplies in the past week.
RTE's website showed that at least 9 nuclear reactors reported unplanned outages after the workers voted Wednesday evening, Reuters reported.
In the past week French workers led by the CGT have blocked oil refineries around the country in protest at the planned reforms aimed at making it easier for firms to hire and fire, which has led to fuel shortages in large parts of the country and long lines of cars at near-empty gas stations.
France produces about three quarters of its electricity in 19 nuclear plants run by state-controlled utility EDF.