British Olympic chief Craig Reedie has denied reports of a deal between London, Madrid and New York ahead of the 2012 Olympics vote.
It has been suggested each city might advise its backers to vote for one of the other two - at the expense of Paris - if it is eliminated early on.
"I can assure you that we are not under any circumstances involved in that kind of exercise.
"You simply cannot have people 'ganging up' on someone else," said Reedie.
"It is difficult enough to get a member to vote for you, and it's absolutely impossible to get a member who wanted to vote for you and couldn't to vote for someone else. It's not on."
International Olympic Committee members will vote to choose the 2012 host city on Wednesday, with a contender dropping out in every round until one has an absolute majority.
Paris is considered the favourite to win, but the next 48 hours will see the French capital and London, Madrid, New York and Moscow all lobbying fiercely for votes.
Strict bidding rules introduced in the wake of the Salt Lake City Winter Games voting scandal prevent rival cities from directly criticising each other.
But Reedie, who is one of Britain's three IOC members, believes the regulations may have to be reviewed once the 2012 selection process is over.
Earlier in the day, two Olympic experts had criticised Paris' main stadium at a London 2012 news conference.
"This is the hottest contest the IOC have ever had and that it's unlikely we will get five cities in a race like this again in the future," said Reedie.
"My guess is that the IOC will review the process after this selection process is completed.
"I think on balance that they may be a little surprised that the hope that nobody would speak ill of another candidate city is very difficult to achieve when there is such huge media interest.
"I think, however, that when you look at the records over the last few months, very few cities have spoken about another candidate city at all.
"There is good spirit among the candidate cities and they get on extremely well.
"But I do think the IOC will review the process because this is the best race they have ever had."