The Football Association has written to Manchester United manager Sir Alex Ferguson and his assistant Carlos Queiroz asking them to explain their comments after Saturday's FA Cup sixth round defeat to Portsmouth.
Ferguson launched a furious tirade after the dramatic 1-0 defeat about referee Martin Atkinson and referees' chief Keith Hackett.
Queiroz has also been asked to explain his comments about Atkinson with both men given until 19 March to respond.
Ferguson was furious that United were denied a first-half penalty when Cristiano Ronaldo went down in the box under a challenge from Sylvain Distin.
The veteran Scot's mood was not improved by the second-half dismissal of Tomasz Kuszczak with the substitute goalkeeper's foul on Milan Baros leading to Pompey's winner from the penalty spot.
Afterwards, Ferguson said: "It's absolutely ridiculous. I can't explain it. Managers get sacked because of things like that and he's going to referee a game next week.
"Martin Atkinson will referee next week, no problem, but his performance today should not be accepted in our game.
"I agree with Sepp Blatter. The standards in our game as opposed to the continent - the tolerance level - is behind Europe. I think it's a big problem. They had great confidence to hang on knowing the referee was on their side.
"Lassana Diarra had eight or nine fouls in the match. It's incredible. I've got to agree with Arsene Wenger. Someone is going to get a serious injury in our game. He's had one himself with Eduardo Da Silva.
"It's not a nice thing to talk about, but the treatment Ronaldo is getting, I'm worried about him.
"Keith Hackett is in a nice, comfortable position and does nothing really. I don't think he makes a contribution to the referees' performances in our country."
Meanwhile, Queiroz had said: "I feel sorry that the game has moved to the situation where referees deserve red cards.
"This referee deserves somebody to come to the side of the pitch after five minutes, give him a red card and pull him out of the game. That is my opinion of this robber.
"The referee is a disgrace. We did our job, Portsmouth did their job but the referee didn't. Sadly, we still have referees who don't understand what is the right thing in the game and who they should be protecting."