The Football Association has asked Avram Grant to explain remarks he made which claimed that Premier League referees favour Manchester United.
The Chelsea boss criticised Steve Bennett's refereeing of United's 2-0 final day victory at Wigan.
Grant suggested United received "some coincidences" as Wigan were denied a penalty and Paul Scholes escaped a second yellow card for a challenge.
He has until 28 May to reply to the FA's letter.
Grant has frequently bemoaned match official Mike Dean's decision to show Jon Mikel Obi a 32nd-minute red card before United went on to beat Chelsea 2-0 in September.
The 53-year-old reignited that debate and then drew a link to Bennett's decision-making during United's 2-0 victory at Wigan on Sunday - a result that gave the Red Devils the top-flight crown by two points from Chelsea, who drew with Bolton.
United's Scholes was booked for a challenge on Wigan's Wilson Palacios but when he later blocked the same player he escaped a second yellow card and thereby a dismissal.
There were also claims for a Latics penalty when Rio Ferdinand leaned to block a Jason Koumas shot with his upper arm.
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"There should have been a red card for Scholes on Sunday. Then there was the penalty but it's finished. I congratulate United.
"I do not think the world is against Chelsea, or English football, but in this case there were some coincidences for Manchester United."
Chelsea beat United 2-1 at Stamford Bridge in April to help ensure the title race went down to the final day, although United had a superior goal difference.
The Blues' 1-1 draw with Bolton on Sunday meant that, with hindsight, all Ferguson's side needed at Wigan was a point but Grant was still unhappy with the decision to appoint Bennett to officiate at the JJB Stadium.
"I looked at the game and (the referee) was, as expected, good for one team," he added.
"I believe in the tradition of the fair English game. I will not say anything against this but what happened is what I expected."
"This is about next Wednesday and that's why Avram is talking that way"
"In England there are some very good referees - but there are some, a few of them, you can influence," he said.
But United manager Sir Alex Ferguson responded on Thursday: "We didn't get a lot of decisions this season.
"This is about next Wednesday and that's why Avram is talking that way.
"I don't think it's about last Sunday, I think it's about next Wednesday, maybe even next season.
"I could have gone on and on and on with decisions because they're all debatable at the end of the day. We feel we didn't get a lot of decisions this season.
"Maybe when we went to Chelsea we should have been champions before that but now the season's over, we'll put it to the back burner."
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