Reuters reports that Enel has now followed up its initial letter of complaint that it sent when the deal was first announced in February 2006. It is thought that Enel’s concerns center primarily on the consequences for the Belgian market, where Suez controls several leading players at different stages of the energy value chain, including power firm Electrabel and gas distributor Distrigas.

Gaz de France meanwhile owns a 25% share in SPE, Belgium’s second largest electricity supplier.

EU competition commissioner Neelie Kroes is set to release the first draft of her review of the Suez-GdF deal on July 3.