An Asian Football Confederation (AFC) official, speaking on condition of anonymity, told AFP that delegates from "nine or 10" of the 46 federations due to take part had left Zurich in protest at bin Hammam's treatment.
"I can tell you that so far delegates from nine or 10 federations have gone home after arriving here," the official said, declining to name the countries involved.
"There is a deep sense of outrage amongst all of the delegates I have spoken to about the actions of the FIFA ethics committee. They have exceeded their mandate," he added.
AFC president bin Hammam, who had been bidding to end FIFA president Sepp Blatter's 13-year reign at the head of world football, has been barred from Wednesday's election pending a corruption investigation.
However, bin Hammam has urged all officials to stay put and follow through on the vote.
"I have told the Asian delegates not to boycott the congress," he said.
Bin Hammam was suspended from all football activities along with Caribbean, Central and North American (CONCACAF) chief Jack Warner following allegations they attempted to buy votes in the campaign to oust Blatter.
FIFA's ethics committee ruled there was no evidence to justify an investigation into Blatter however, a factor that has angered Asian delegates.
"They have censored and suspended two heads of federations but on the other side have completely ignored anything about Sepp Blatter," the official said.
Blatter is now poised to win a fourth and final term as FIFA chief when he stands unopposed for re-election at FIFA's congress on Wednesday (local time).
Asian delegates declined to say whether they would stage a protest at the congress similar to their walkout in 1999, when they dramatically stormed out of a meeting in Los Angeles over World Cup places.
"There is no feeling as yet about a walkout. We don't want to politicise FIFA because it has suffered immensely," the FIFA official said.
"But there is no question that the election has been tainted."
AFC vice-president Ganesh Thapa meanwhile said bin Hammam had been excluded from the FIFA race for "political reasons".
"My personal feeling is that they were worried by Mohamed bin Hammam so they took him out. It's politics."
- AFP
Tags: sport, football, switzerland