BNP Paribas SA dropped as much as 10 per cent in Paris trading after a Belgian court froze the bank's plans to buy Fortis assets for €14.5 billion ($19.5 billion).

The Brussels Court of Appeals ruled 12 December that the sale of Fortis assets must be put to investors for a vote before 12 February, complicating BNP Paribas's plan to complete the purchase quickly and preserve the customer base of Brussels-based Fortis NV. The court also ordered Paris-based BNP Paribas, France's largest bank, to keep funding Fortis Bank to prevent a collapse before the vote.

In other words, the court ruled that shareholders must be given a say in the dismantling of Fortis ordered by the Dutch, Belgian and Luxembourg governments in October to inject capital into its parts. "The government will examine ... which way to take in this new situation," it said in a statement after an extraordinary meeting on Saturday. A prosecutor is to report soon on whether Fortis' carve-up followed proper procedure. (See: Benelux governments inject €11.2 billion to save Fortis)

According to the court decision, the Belgian state would be forbidden to sell Fortis assets to BNP Paribas before 16 February 2009 and would face a €5 billion penalty if it did. BNP would be obliged to maintain its inter-bank support for Fortis Bank, the arm in which it was to buy a majority stake.

A spokesman for Belgian Prime Minister Yves Leterme said the government would take its decision on Monday evening and that appealing to the Supreme Court was an option. Fortis CEO Filip Dierckx expressed surprise on Saturday at the court decision, saying he believed the break-up operation would be successful. "We believe we can create value and it is important for our clients. We have to follow that way," he said.

The ruling came after a group of Fortis minority investors sued to suspend the deal. Fortis may be worth more than when it was forced to sell most of its assets to BNP, said Laurent Arnauts, a lawyer for the plaintiffs. He said that Fortis shareholders would seek a higher offer for the financial services company, Belgium's biggest.

"This is a major victory for shareholders that have been deprived of their most essential rights," Mischael Modrikamen, another lawyer for the shareholders, said. A spokesman for Dutch finance minister Wouter Bos said that the minister believed that the Belgian court ruling had no consequences for the Dutch position. "The deal has been done. If Fortis shareholders don't agree, that is between Fortis and its shareholders. We are not involved," he said.

BNP Paribas said on Friday it was still planning to close its deal to buy a majority stake in Fortis soon.

"This decision in no way calls into question the interest of this deal," the French bank said in a statement.

Shares in Fortis have fallen to less than € from almost €30 in April 2007 when it launched its ill-fated joint bid for Dutch rival ABN AMRO, prompting the legal action. Shareholders rejected a proposed chairman at rowdy meetings earlier this month as they voiced their anger at executives they hold responsible for their losses. They also argue they were short-changed by the state-led carve-up.