The FIFA executive committee -- with president Sepp Blatter and vice president Michel Platini both suspended -- is holding two days of talks to discuss reforms proposed by top sporting official Francois Carrard who was named by the world body.
But top sponsors Anheuser-Busch, Adidas, Coca-Cola, McDonald's and Visa said reforms should be "subject to independent oversight".
The multi-nationals are reportedly angry that they have not been given places on FIFA's reform committee. They have in the past threatened to review their football deals.
- Reform doubts -
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The executive committee will decide whether to send the reform package for adoption at a special FIFA congress on February 26, when Blatter's replacement will be chosen.
The meeting is being held on the fifth anniversary of the 2010 vote that controversially awarded the 2018 World Cup to Russia and the 2022 tournament to Qatar.
That decision set off a cascade of allegations of corruption and political skullduggery.
Sponsors are not the only group to express concern over the reform measures being undertaken by FIFA.
"We urge you to embrace positive changes and also recognize that this is just one step toward creating a credible future for FIFA," the sponsors said in a letter to the world body.
"Transparency, accountability, respect for human rights, integrity, leadership and gender equality are crucial to the future of FIFA. Reforms can set the proper framework for these characteristics, but a cultural change is also needed."
Other groups also doubt the Carrard panel, dominated by officials nominated by regional confederations, will be able to press through convincing reforms.
"What is actually needed is an independent set of executives that have no ties in world football, walking in and cleaning this place up," said Declan Hill, author of "The Fix: soccer and organised crime".
The Transparency International activist group's chief Cobus de Swardt predicted Carrard's committee "will likely avoid taking some hard decision about changing the way FIFA does business", because doing so could affect the committee members themselves.
Warner, a businessman, politician and former kingpin in Caribbean football and in the American confederation, is accused of taking millions of dollars in underhand payments from various sources.
A former FIFA vice president, he was banned for life by the world body in September.