LONDON - A London court may decide on Friday whether to protect Telenor's TEL.OS voting rights in a decision that could derail a $6 billion (S$7.6 billion) telecoms deal and re-ignite tensions with Russia's Alfa Group.

Norway's biggest telecom company is seeking an injunction to prevent the dilution of its 36 per cent stake in Vimpelcom VIP.N , Russia's second largest cellphone group, to the benefit of old rival and co-owner Mikhail Fridman's Alfa Group.

Alfa and Telenor ended years of acrimony in 2009, when they combined their telecom holdings to form Vimpelcom.

Vimpelcom is planning to buy control of emerging markets-focused Orascom Telecom ORTE.CA and Italy's Wind from Egyptian-born telecom tycoon Naguib Sawiris, a deal that Telenor is fiercely resisting.

Alfa Group is backing the transaction, but Telenor says it does not make financial or strategic sense.

A ruling by London's Commercial Court in favour of Telenor would open the door to a long-running arbitration process, which would test Sawiris's patience, bankers said.

"Arbitration between Vodafone and the Polish shareholders in Polkomtel took about three years. These things are not resolved quickly," said a banker who advises European telecom companies.

The deal, which will be put to a shareholder vote on March 17, would give Sawiris 30.6 per cent of the voting rights in the enlarged group, and cut Telenor's rights to 25 per cent.

"If arbitration takes longer than six months, there is a real risk that Sawiris will look to sell to someone else," said Tim Daniels at broker Olivetree Securities.

Sawiris needs a deal because he is blocked from repatriating profits from Djezzy, Orascom's main revenue earning unit that the Algerian government plans to nationalize.

The tycoon is fighting a bitter and costly battle over taxes with the Algerian authorities, and the clock is also ticking on his maturing debt, totalling about $3 billion (S$3.85 billion) for Orascom alone over the next three years.

If Telenor wins the injunction, Vimpelcom must put enough new shares into an escrow account so that Telenor's stake would not change if the deal is voted through by investors.

But Telenor would only get the shares if it won the subsequent arbitration case.

In a deal like this, existing shareholders normally expect to be able to exercise pre-emptive rights and subscribe to new shares on a pro-rata basis.

Vimpelcom is claiming the deal is not subject to pre-emption rights, because a subsidiary of Alfa already owns shares in Orascom, creating a loophole that means existing shareholders cannot buy into new share issues.

Telenor stands only a small chance of stopping the deal with Sawiris if it loses the injunction, another banker said.

It will then go to the investor meeting, where it may be voted through, Telenor Chief Executive Jon Fredrik Baksaas has said.

"We are a shareholder in Vimpelcom and whether we remain (if the deal goes through) is a question that remains to be considered," he told Reuters previously.