Roberto Martinez's comments after Wigan's 4-0 defeat to Manchester United have earned him a £10,000 fine from the Football Association.
Martinez claimed United had received favourable treatment from referees on several of the Latics' previous trips to Old Trafford and that his side were measured differently by officials on those occasions.
The Spaniard, who was left particularly frustrated by Michael Oliver's decision to award Danny Welbeck a penalty, admitted the misconduct charge and was warned about his future conduct.
Speaking to reporters after the match, Martinez said: "You know what he (Welbeck) is trying to do. I have come to United three times before today and for whatever reason we don't seem to be measured in the same manner as the team at home.
"Today the penalty is as bad a decision as you are going to see in the Premier League. In many ways, you feel as though you are fighting against a mountain."
A statement on the FA website read: "The charge was in relation to a breach of FA Rule E3 concerning media comments which implied that the match referee and/or match officials in general are motivated by bias and/or brought the game into disrepute.
"Martinez, who had requested a personal hearing, was also warned as to his future conduct.''