Italy's competition watchdog last year ordered Enel and two subsidiaries to pay a 93 million euro ($106 million) fine, levied on its operations in a part of Italy's power market.
The fine was later reduced to 27.5 million euros after an appeal by the energy group. Enel denies any wrongdoing and appealed to overturn the reduced penalty.
Enel on Monday said in a statement that data and analysis it had provided to show it did not harm competition were not taken into account by the antitrust authority.
"Enel remains convinced that it has acted in full compliance with the rules of commercial conduct," it said.
The EU Court of Justice must clarify some aspects of European legislation regarding market abuse, which are important for assessing Enel's appeals, the administrative State Council court said in a ruling seen by Reuters.
($1 = 0.8743 euros)
(Writing by Giulio Piovaccari, additional reporting by Stephen Jewkes; Editing by Andrew Cawthorne and Barbara Lewis)