Salford City Reds have been docked two points and fined £5,000 for fielding 14 players during the clash with Castleford Tigers on 27 April.
A Rugby Football League Appeals tribunal handed down the increased sanction after Salford failed in their appeal against the initial punishment of a £10,000 fine.
The sanction relates to an incident in the 77th minute of the match at the Salford City Stadium, which the hosts won 34-30.
Salford player Darrell Griffin and the player who was replacing him from the bench, Vic Mauro, were both involved in tackles while the Reds had 14 players on the field of play.
The points deduction means Salford drop below the London Broncos to the foot of the Super League table.