Salford City Reds have been deducted two points and fined £5,000 after fielding an extra player during their Super League game against Castleford Tigers.
A RFL tribunal rejected the clubs appeal and increased the club's original punishment.
The original punishment was a £10,000 fine, although that has been halved, the club has been deducted two points. It means Salford are now bottom of the Super League as they drop one point behind London Broncos.
The incident came in the match against Castleford when Darrell Griffin and his substitute replacement Vic Mauro were both involved in tackles towards the end of the match on April 27.
Salford eventually won the match 34-30 to lift them off the foot of the table but will drop back down to the bottom after having 14 players on the field.
The RFL investigated the incident after Castleford lodged a complaint with chief executive Steve Gill stating that three plays took place with Salford having 14 men on the pitch.
There were many complaints for the League initially failing to dock Salford points with Warrington's coach Tony Smith criticising the RFL.
"I would hate to have lost that game because our opponents had an extra man out there," he said to BBC Sport.
"I just think it sends out a poor message, that if you are prepared to pay for it then you can get away with it."
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