"There will be an effect but I don't think it will have alarming consequences because Italian banks are robust and the important thing is that the market is competitive," Gian Maria Gros-Pietro told reporters at the European House Ambrosetti business forum in Italy on Friday.

Gros-Pietro later told reporters that the bill was likely to be under a billion euros for Intesa, adding that a more precise estimate could not be given until the windfall tax has been approved by parliament.

The windfall tax, which wrongfooted bank investors when announced in August, is a one-off measure targeting gains from higher interest rates. The government subsequently clarified that the tax would not amount to more than 0.1% of a bank's total assets.

The Treasury expects to draw less than 3 billion euros from the measure, sources have said.

Gros-Pietro said dividends would inevitably be affected by any impact of the tax on profit but that Intesa investors would still be well rewarded.

($1 = 0.9252 euros)

(Reporting by Elvira Pollina and Giulio Piovaccari, writing by Keith Weir, editing by Alvise Armellini and Louise Heavens)