BRUSSELS - Fortis was set on Wednesday to postpone a shareholder vote on the sale of its former banking arm to BNP Paribas, casting fresh doubt over whether it can complete the deal.

Fortis investors, who blocked BNP's purchase of 75 percent of Fortis Bank from the Belgian state last month, were set to vote on revised conditions for the deal at meetings in the Dutch city of Utrecht on April 8 and in Brussels on April 9.

However, the Brussels Court of Appeal ruled on Tuesday that only shareholders who held stock at the time of the break-up of Fortis in October would be allowed to vote at the Brussels meeting.

The ruling could swing the vote in favor of the no camp, as well as giving Fortis organizational headaches. Shareholder registrations for the meetings close on Thursday.

It is likely that the (Brussels) shareholder meeting will be postponed. The board will make a decision this afternoon, Fortis spokeswoman Kathleen Steel said on Wednesday.

A BNP spokesman declined to comment.

Fortis has meanwhile decided to launch an appeal against Tuesday's court ruling. That is set to be brought before the appeal court on Thursday.

At 9:15 a.m. EDT Fortis's shares were down 3.3 percent at 1.3370 euros, while the DJ Stoxx European banking sector index .SX7P was up 0.7 percent. BNP Paribas shares were up 0.9 percent at 31.41 euros.

Fortis was carved up by the Belgian, Dutch and Luxembourg governments in October after an 11.2 billion euro ($14.80 billion) cash injection failed to calm investors.

The Dutch business has already been taken over by the Netherlands and Belgium owns the Belgian banking arm Fortis Bank. But BNP's planned purchase of most of Fortis Bank from Belgium and a part of Fortis Insurance Belgium from Fortis itself is in limbo.

INCREASED CHANCE OF 'NO' VOTE

The court's ruling that only investors who held shares on October 14 are eligible to vote increases the chance of a 'no' vote. This group rejected the BNP deal by a tiny 50.26 percent in February.

If repeated, many analysts believe BNP would walk away from the deal. Fortis would be left with its insurance operations, with its banking arms still in state hands, and potentially a far larger amount of toxic assets.

Analysts argue that more recent shareholders, including hedge funds, would be more inclined to vote 'yes' given that they are eyeing potential profits, rather than huge losses.

KBC analyst Dirk Peeters said the ruling meant that the group of shareholders eligible to vote was becoming ever smaller and that the influence of Fortis's largest shareholder Ping An (601318.SS), which voted 'no' in February, was growing.

The Chinese insurer, which owns 4.99 percent of Fortis, is expected to announce later this week how it will vote.

Bank Degroof analyst Ivan Lathouders said a postponement of the shareholder meetings might also force a renegotiation with BNP Paribas of the current April 18 deadline to close the deal.

Rabo Securities analyst Cor Kluis said he saw no reason why BNP would not agree to move the deadline. However, he said later meetings might take place in a different economic climate.

Half a year ago nobody wanted to keep the bank. In a month's time that might be different ... but if the market crashes BNP may also think twice about whether it still wants to go ahead with the deal, he said.

Rabo cut its rating for Fortis to hold from buy on Wednesday, reflecting the added uncertainty.

Fortis reported a 28 billion euro net loss for 2008 on Tuesday on the state takeover of its troubled banking activities, but argued it had a viable future as an insurance group.

(Additional reporting by Matthieu Protard in Paris; Editing by Philip Blenkinsop, Greg Mahlich)

($1=.7567 euros)

ABN Amro Investment BNP Paribas