The Norwegian news agency NTB has seen the letter between the European and international football federations.
The letter contains questions, accusations and requests for documentation. Uefa writes that Fifa must respond by November 2, a deadline that several media outlets have previously reported.
"These questions require answers now. They cannot be postponed until the next meeting of the FIFA Council," the letter says, further straining the tense relationship between the federations.
Many of the points in the letter concern the now-scrapped plans to sell shares in the World Cup to private investors through a company called Fifa Forward Enterprise (FFE).
Here are some of the points related to FFE:
+) Does Gianni Infantino, the FIFA president, think that FFE was a good idea and, if so, on what grounds?
+) When was the idea for FFE first conceived?
+) Will FIFA accept an independent review of the FFE process, including the FIFA president's own role?
+) Why has Fifa opposed UEFA's request for access to documents regarding FFE and the lawsuit filed in the US?
Lifted suspension
The letter contains other types of questions. Among other things, UEFA wants answers about what really happened in the high-profile so-called Balogun scandal at the World Cup, when US President Donald Trump claimed that he had called Gianni Infantino to have American striker Folarin Balogun's suspension lifted.
Here are some of the points about Balogun:
+) President Trump has confirmed that he called the FIFA president to request a review of the disciplinary case involving Balogun. What specifically did he ask for, and what was the FIFA president's response?
+) Can Fifa provide the full written justification for the decision in the Balogun case?
Questions about the half-time break
The letter also contained questions on other topics. Here are some examples:
+) The half-time break in the World Cup final lasted 27 minutes, without the question being put to the international rules body IFAB and without consultation with the FIFA Council. Similarly, mandatory fluid breaks were introduced in all World Cup matches in violation of current regulations - apparently without consultation with or approval from IFAB.
+ ) Many reports in recent years have raised questions about the FIFA president's use of private planes and the cost of his accommodation, particularly in Qatar and the United States.
+) We (Uefa) are requesting access to the list of guests who sat in the VIP seats during the World Cup final.
Uefa does not specify what measures it will take if Fifa does not meet the deadline for responses.