Sources with direct knowledge of the matter told Reuters.
The program, valued at tens of billions of euros, is central to France's plan to renew its aging national nuclear fleet and would add approximately 10 gigawatts of capacity, with the first reactor scheduled to come online in 2038.
According to the sources, the probe is expected to be launched next month.
At the end of last year, France submitted a request to Brussels for approval of the state support, which includes a subsidized loan covering at least half of the construction costs for the six nuclear reactors.
The new facilities would replace older nuclear plants and secure future energy supplies to meet rising demand over the next decade, driven in part by the energy requirements of data centers.
However, EU regulators want more time to examine this complex project, one of the largest public interventions in the country in recent years, the sources explained.
Brussels fears that the six new plants could further strengthen the market share of EDF, which already accounts for over 75% of net electricity production in France.
The Commission, the French Energy Ministry, and EDF declined to comment.
The project, announced in 2022, now has an estimated cost of 72.8 billion euros at 2020 prices.
An in-depth EU investigation would also allow the Commission to build an unassailable case should the anti-nuclear Austrian government decide to take legal action against the project's approval, a scenario that some officials believe is likely, one of the sources said.
Vienna has previously challenged state aid for nuclear projects in Hungary and the United Kingdom.
(Translated by Jasmine Mazzarello, editing Andrea Mandalà)
