A prominent member of the FIFA ethics commission has resigned his post in protest at what he perceives to be a lack of determination to stamp out corruption.
The 67-year-old said in the letter: "The events of the past few weeks have raised and strengthened the impression that responsible persons in FIFA have no real interest in playing an active role in resolving, punishing and avoiding violations against ethic regulations of FIFA."
Corruption within FIFA was exposed last year and led to the suspensions of executive committee members Amos Adamu and Reynald Temarii from any football activity.
FIFA's investigation revealed more widespread concerns with four other officials - all former executive committee members - also banned.
Nigeria's Adamu became the first FIFA member ever to be suspended for bribery when he was banned for three years and fined 10,000 Swiss francs by the body's ethics committee, though he vowed to appeal.
Adamu was found guilty of asking for money in return for his World Cup vote after he asked undercover Sunday Times investigators to channel cash for a project through a family company.
Fellow executive committee member Temarii, of Tahiti, was suspended for a year and fined 5,000 Swiss francs for breaching rules on loyalty and confidentiality, something he also denied.
The other officials sanctioned were Ismael Bhamjee of Botswana, who was handed a four-year ban, Amadou Diakite of Mali and Ahongalu Fusimalohi of Tonga who were suspended for three years, and Tunisian official Slim Aloulou who was suspended for two years.
All four were also fined 10,000 Swiss francs.
Earlier on Sunday, British Prime Minister David Cameron attacked the "murky" world of football governance - saying publicly that he was personally misled by a number of FIFA executives over England's failed 2018 World Cup bid, with Russia being named as hosts for the event.
Qatar were then controversially handed the 2022 tournament.
Cameron said some reneged on assurances that they would support the bid - which eventually received only two of the 22 votes available.
He gave only a lukewarm welcome to assurances by FIFA chief executive Sepp Blatter that he would set up an anti-corruption unit.
"We had a great bid - technically I think by far the best bid and I think the presentation we made was compelling," he told BBC Radio 5 Live.
"I definitely had a number of those FIFA executives who looked me in the eye and shook my hand and said 'don't worry, we're with you'.
"I'm afraid that the world of football governance is rather murky in that way."
Asked about Mr Blatter's anti-corruption efforts, he said: "I think we will have to judge that by the results."