ROME- Italy's competition watchdog said on Wednesday it had fined three gas and power retail sellers, including Eni and Enel , a total of 12.5 million euros ($15 million) for the unjustified rejection of client claims not to pay bills due to late invoicing.

In a statement the watchdog said it had fined Enel Energia 4 million euros and Eni Gas e Luce 5 million euros for unfairly not accepting the statute barring of bills relating to consumption dating back more than two years.

Enel said in a statement it "had always acted in full compliance with primary and regulatory legislation" and it reserved "all actions for its own protection".

Eni also rejected the decision saying that it was "carefully considering an appeal". ($1 = 0.8267 euros)

(Reporting by Francesca Piscioneri, editing by Stephen Jewkes) ((francesca.piscioneri@tr.com; +390680307713;))