Fortis executives twice had to stop the meeting in Ghent, Belgium
Shareholders in Fortis booed, threw shoes and walked out of its general meeting in Ghent as they called for the company's executives to resign.
Some investors were angry about the sale of Fortis Bank to BNP Paribas, saying it was the latest Belgian firm to be sold to a French company.
However, the result of the vote showed that 73% were in favour of the deal.
The Belgian, Dutch and Luxembourg governments rescued Fortis in October, and decided to break up the group.
Lawyer Mischael Modrikamen, representing about 2,400 shareholders, led the walkout and warned of legal action against the vote.
He says it violates Belgian company law and should be restricted to those who held shares before October.
But Fortis executives said they could not exclude recent shareholders from joining the vote.
Fortis' banking operations are now in the hands of the Belgian government and chairman Jozef De Mey said current management had "no room to manoeuvre".
However shareholders must still vote on the sale after a court ruled that the government was wrong to sell parts of the bank without their permission.
In order for the deal to be approved, a majority of shareholders at a second meeting in the Dutch city of Utrecht on Wednesday must also vote in favour of it.
The result may be similar though, given that shareholders can vote at both meetings.