Nottingham Forest have failed in their appeal against a £750 000 ($968 000) fine imposed for a social media post last season that took aim at Premier League match official Stuart Attwell.
Forest published the post last April after a 2-0 defeat to Everton in the Premier League, a match in which the club felt they were denied three clear penalties.
The club said they had "warned" referees' body Professional Game Match Officials Limited (PGMOL) that Attwell, who was the video assistant referee for the match, was a fan of their relegation rivals Luton, adding: "Our patience has been tested multiple times."
A regulatory commission issued a £750 000 fine in October, with Forest immediately indicating their intention to appeal, arguing the punishment was disproportionate.
The Football Association described the post as an "egregious, direct and public attack" on Attwell and an attack on referees in general "on an unparallelled scale".
The FA confirmed on Monday that an appeal board had upheld the original sanction and had ordered the post to be taken down.
The link to the post on X was not working on Monday, though the club did not immediately confirm it had been taken down.
The appeal board said in its written reasons: "The (original) commission was entitled and right to give very considerable weight to the need for deterrence and the fact that NFFC had no mitigation. The lack of mitigation was particularly striking."
Forest escaped relegation last season, while Luton went down to the Championship.
This season, Forest are third in the Premier League table and challenging for a Champions League place.