The two companies formally gave notification of their merger plan to the European Commission on Friday, according to a filing on the EU executive's website, with a decision due by March 11.

The proposed merger of 3 Italia SpA and Vimpelcom's WIND Telecommunicazioni is expected to come under close scrutiny because it will reduce the number of mobile network operators in Italy from four to three, a reduction which competition regulators think could lead to higher prices for phone users.

But Hutchison argues that by cutting costs the new combination of WIND and 3 Italia would be a more effective competitor against Telecom Italia and Vodafone.

The Hong Kong conglomerate, whose last two acquisitions in Austria and Ireland brought a similar reduction in the number of operators and were cleared only after it agreed to make concessions, said it was confident of getting approval for the Italian deal.

"This transaction will ensure that there is a strong third player in the Italian market that is able to compete head-on in the market place against the two larger operators," it said in a statement.

Russian billionaire Mikhail Fridman's LetterOne fund owns 47.9 percent of Vimpelcom's voting rights.

The Commission can either clear the deal, with or without conditions, or open a full-scale investigation if it has substantial concerns.

Hutchison may have to offer concessions similar to those granted with 3 Group's acquisitions of O2 in Ireland and Orange Austria, said Brussels-based competition lawyer David Cantor.

"Italy lacks a robust mobile virtual network operator segment, relatively speaking, and it's therefore very likely the Commission will insist on the creation of a new 'fourth MNO' as a condition of clearance of WIND-Three," he said.

The EU competition regulator last week warned Hutchison of the concerns it had for competition in the UK market from Three's proposed 10.3 billion pound ($14.93 billion) takeover of Telefonica's O2 UK, which will also reduce the number of mobile network operators there to three from four.

Hutchison is expected to offer concessions later this month and may seek a closed-door hearing where it will seek to persuade senior Commission officials and national competition agencies of the merits of the deal. The Commission is scheduled to rule on the case by April 22.

"Regardless of whether the Commission buys into Hutchison's recent promise to sell off network capacity to UK retail competitors post-merger, it's a good bet that clearance will require the merged company to exit one of the two prevailing UK network-sharing platforms," Cantor said.

(Reporting by Foo Yun Chee; editing by Louise Heavens, Greg Mahlich)

By Foo Yun Chee