FIFA said on Wednesday it had begun ethical proceedings against Bin Hammam, the Qatari head of the Asian Football Confederation, along with CONCACAF president Jack Warner and two other officials.
All four have been summoned to appear before FIFA's ethics committee on Sunday, three days before the vote for the most powerful job in world soccer, in response to a report from Chuck Blazer, CONCACAF's general secretary, and another executive committee member.
Bin Hammam and Warner issued statements denying any wrongdoing.
FIFA said Blazer's report, which included "bribery allegations", referred to a Caribbean Football Union (CFU) meeting attended by Warner and Bin Hammam on May 10/11 and was linked to the election campaign.
Bin Hammam strongly denied any wrongdoing and said he was confident he would still be allowed to stand in the June 1 vote, when he is the only challenger to Blatter.
"This has been a difficult and painful day for me today," Bin Hammam said in a statement. "But, if there is even the slightest justice in the world, these allegations will vanish in the wind.
"This move is little more than a tactic being used by those who have no confidence in their own ability to emerge successfully from the FIFA presidential election.
"Here I completely deny any allegations of wrongdoing either intentionally or unknowingly while I was in the Caribbean.
"I am confident that there is no charge to answer and that I will be free to stand in the FIFA presidential election on June 1 as originally planned."
Warner was quoted on The Daily Telegraph website as telling the British newspaper he "was unaware of any wrongdoing on my part" and implied the charges were linked to the presidential election, in which Blatter is standing for a fourth term.
"I take note of the initiative by FIFA'S Ethics Committee and confirm that I have been invited to attend a hearing this week Sunday, May 29, 2011 in Zurich," Warner told the newspaper.
"I am unaware of the particulars of the matter being investigated by FIFA at this time, so I will therefore abstain from any comment until such time as I have been made aware of all that has been submitted to FIFA.
"It is interesting to note the timing of these allegations and the hearing scheduled days before the FIFA presidential elections.
"As this is now a formal procedure, I shall not be offering any further comment prior to the hearing on Sunday."
The meeting referred to by FIFA was organised so Bin Hammam could state his election case to delegates. He had been unable to attend the CONCACAF Congress in Miami on May 3 after being denied a visa for the United States.
Bin Hammam has used the campaign to call for reform at FIFA, which has been mired in claims of corruption surrounding last year's vote to choose hosts for the 2018 and 2022 World Cups.
WITHIN FIFA
Unlike last year's scandal, in which two executive committee members were banned following investigations by Britain's Sunday Times newspaper, the allegations came from within FIFA for the first time.
CONCACAF, the North and Central America and Caribbean Confederation, holds 35 of the 208 votes at the FIFA Congress which will choose between Bin Hamman and incumbent president Blatter.
Warner has always been regarded as a staunch Blatter supporter but said his confederation had not yet chosen who it would back this time.
FIFA would not comment on whether the election might now be postponed.
Spokesmen for Blatter and CONCACAF also said they would not comment.
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