"Instead of calling into question the startling failure of this opening up of the market, the government has decided to sacrifice EDF," said the unions in a joint statement.
The CEO of EDF on Monday expressed "real shock" and indignation after EDF was told to sell more power to rivals at below-market prices in a bid to head off public anger against rising power bills in a French election year.
The French state owns 84% of EDF's shares. The group forecast last week that the government decision would knock around 8 billion euros ($9.1 billion) off its 2022 core earnings before interest, taxes, depreciation and amortization.
($1 = 0.8778 euros)
(Reporting by Dominique Vidalon; Editing by Sudip Kar-Gupta)