The new 72bn euro ($85.3bn; £48.9bn) operation will be 34%-owned by the French state and is expected to deliver annual cost savings of 500m euros.
Italy has complained strongly that the merger is aimed at blocking a possible takeover of Suez by Italian firm Enel.
Prime Minister Silvio Berlusconi called on the European Union to intervene.
Italy’s Economy Minister Giulio Tremonti is expected to meet with the EU’s Competition Commissioner Neelie Kroes in Brussels on Tuesday.
Other Italian government officials also have also been voicing their concerns about French protectionism.
In an interview with La Stampa newspaper, Italian Industry Minister Claudio Scajola said Italy would ask the European Commission to examine the French government’s backing of the merger.
“We are facing an enormous violation of the EU rules and the rules of the free markets,” said Mr Scajola, adding that Italy would only turn to retaliatory measures as a last resort.