In a memo to managers seen by Reuters, Jean-Bernard Levy said he had tried to persuade ministers to adopt a different course, and was now looking at steps to defend EDF's interests.
Shares in the firm slumped as much as 25% on Friday after the government of President Emmanuel Macron - facing a re-election battle in three months and keen to head off public anger over rising power bills - ordered the utility to sell more cheap nuclear power to rivals.
"This is not what we had proposed to the government," Levy said in the internal memo. Instead, he said, the firm had recommended targeted help for small businesses and the most vulnerable industrial users.
"Having fought hard against it, this decision comes as a real shock," he said of the government move. "Naturally, we have to deal with it. It is going to weigh very heavily on our results."
Referring to the government measures, combined with technical problems at several nuclear plants that forced them offline, Levy wrote: "This news is rocking the company."
"Many of you have shared with me your support, and even your indignation, and I share your emotions. You should know that the executive committee and I remain very combative," he said.
"Together with the executive committee, we will study the appropriate measures to reinforce the balance sheet of the group, and all measures that protect its interests. At stake is our capacity to safeguard our strategic development. We plan to make these measures public within a month."
The French state owns 84% of EDF's shares. The group forecast last week the government decision would knock around 8 billion euros ($9.13 billion) off its 2022 core earnings before interest, taxes, depreciation and amortization.
($1 = 0.8764 euros)
(Reporting by Benjamin Mallet Writing by GV De Clercq Editing by Christian Lowe and Mark Potter)
By Benjamin Mallet
