A source close to one of the 11 sides behind the letter said it had requested “full disclosure” of United’s scouting techniques and included a series of questions about the dispute which arose before Leeds’ clash with Derby County 10 days ago.
The Elland Road club are under investigation by both the EFL and the Football Association after a member of Marcelo Bielsa’s backroom team was stopped by police outside Derby’s training ground 24 hours before County lost 2-0 at Elland Road on January 11.
Derby made a formal complaint soon after that fixture but 11 teams joined together to write to the EFL on Friday after being angered by comments made by Bielsa during a 66-minute media briefing at Thorp Arch last week.
Bielsa confirmed that he had sent scouts to watch every Championship side train this season but used his briefing at United’s training ground to hit back at claims that he had gained an unfair advantage by doing so.
Norwich City, Millwall and Blackburn Rovers have so far confirmed that they put their names to the letter.
The YEP understands that Middlesbrough, Bristol City and Nottingham Forest are also among those clubs involved.
Bristol City owner Steve Lansdown called for Leeds to be punished with a points deduction last week but the YP has been told that the letter to the EFL made no mention of possible sanctions.
A source said: “The letter doesn’t mention any punishment. It’s seeking full disclosure about what happened.”
The EFL and FA have made no comment about possible penalties facing Bielsa or Leeds and are still to decide if they will mounts disciplinary action, although individuals involved in the case have played down the possibility of a points deduction.