The Red Devils manager admitted a charge of misconduct after claiming that his side was "having to play officials as well as the oppositions" after losing to Sunderland.
The Scot's punishment is in relation to post-match comments to the media which he made following his side's 2-1 defeat in the first leg of the club's Capital One Cup semifinal at Sunderland on Jan. 7.
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This followed on from a free kick being given against United defender Jonny Evans in the first half, which led to Sunderland's opening goal.
Afterwards, Moyes claimed that his team was "having to play officials as well as the opposition", adding: "It's terrible, it really is. We're actually beginning to laugh at them."
Following an independent regulatory commission hearing on Friday, a statement on the FA's official website read: "Manchester United manager David Moyes has been fined £8,000 and warned as to his future conduct.
"Moyes had admitted an FA misconduct charge in that his post-match comments following his side's game at Sunderland on Tuesday, January 7, 2014 constituted improper conduct in that they called into question the integrity of the match officials appointed to that fixture and/or appointed to Manchester United fixtures generally, and/or implied that such match officials are motivated by bias; and/or brought the game into disrepute, in contravention of FA Rule E3(1)."
Moyes is the latest Premier League manager to face disciplinary action for speaking out against referees this season. Earlier in January, Brendan Rodgers was fined £8,000 for comments made following Liverpool's 2-1 defeat at Manchester City on Dec. 26.
Rodgers labeled the officials' performance as "horrendous" after the game at the Etihad Stadium.