Fifa has been engulfed by allegations of corruption since US authorities indicted 14 officials this summer.
The letter was sent from Adidas, McDonald’s, Coca-Cola, Visa and the Budweiser brewer Anheuser-Busch.
A Fifa spokeswoman said the five sponsors would play an “important role in the reform process”.
Fifa’s suspended president Sepp Blatter has always denied any wrongdoing — but in September, he too was made the subject of a Swiss criminal investigation, launched alongside the US inquiry.
Blatter’s one-time likely successor Michel Platini is also suspended and facing a life ban from football.
The scandal erupted in May, with a raid on a luxury hotel in Zurich and the arrest of seven Fifa executives — conducted at the behest of the US authorities.
The US has indicted a total of 14 current and former Fifa officials and associates on charges of “rampant, systemic, and deep-rooted” corruption following a major inquiry by the Federal Bureau of Investigation (FBI).
‘Cultural change’ is inevitable, according to sponsors.
“We know that you, the Executive Committee members, will soon be considering a list of reforms aimed at strengthening Fifa’s governance,” the sponsors’ letter read.
“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.”
The sponsors were initially promised places on the Fifa reform committee. However, in the end they were offered seats on an advisory board which has yet to be appointed.
But the Fifa spokeswoman said their views would not be ignored.
“We share their passion for the game and are committed to working with them to embrace positive changes so that we can fulfil our mission of promoting football around the world,” she said.
A special Fifa congress is due to be held on February 26 that will select a new president and vote on a reform package drawn up by former International Olympic Committee Director General Francois Carrard. — BBCSport