The 24-hour strike by the energy branch of the hardline CGT trade union is part of a nationwide protest by several unions against President Emmanuel Macron's reforms.
RTE's data showed that power generation was reduced at EDF operated St. Laurent 1, Cruas 2 and Chinon 4 nuclear reactors, while output was at zero at the Cordemais 4 and 5 coal power plants.
The generators were expected to resume production later on Tuesday evening.