Leading FIFA sponsors Coca-Cola and McDonalds have demanded Sepp Blatter's immediate resignation as president.
The two companies have issued statements saying reform at world football's scandal-ridden governing body can only take place with its beleaguered leader out of the picture.
Swiss prosecutors last week opened criminal proceedings against the 79-year-old.
Coca-Cola, one of five top-tier FIFA global partners, said: "For the benefit of the game, the Coca-Cola Company is calling for FIFA president Joseph Blatter to step down immediately so that a credible and sustainable reform process can begin in earnest.
"Every day that passes, the image and reputation of FIFA continues to tarnish. FIFA needs comprehensive and urgent reform, and that can only be accomplished through a truly independent approach."
McDonalds, a second-tier sponsor, said: "The events of recent weeks have continued to diminish the reputation of FIFA and public confidence in its leadership.
"We believe it would be in the best interest of the game for FIFA president Sepp Blatter to step down immediately so that the reform process can proceed with the credibility that is needed."
FIFA's sponsors pour millions of pounds into the organisation and their public calls for change will turn up the heat on Blatter.
He is suspected of criminal mismanagement or misappropriation over a TV rights deal he signed with former Caribbean football chief Warner in 2005 and of "a disloyal payment" in 2011 of two millions Swiss francs (£1.35million on current exchange rates) to current UEFA president and FIFA presidential candidate Michel Platini for work allegedly carried out by the Frenchman between 1999 and 2002.
The pair are also understood to be under investigation by FIFA's ethics committee.
Blatter has denied wrongdoing and on Friday night reinforced his stance that he would not be stepping down straight away.
His United States-based lawyer Richard Cullen said in a statement: "While Coca-Cola is a valued sponsor of FIFA, Mr Blatter respectfully disagrees with its position and believes firmly that his leaving office now would not be in the best interest of FIFA nor would it advance the process of reform and, therefore, he will not resign."