Salford City Reds have been docked two competition points for having 14 players on the pitch during their Super League win over Castleford Tigers on April 27.
The Reds were initially fined £10,000 after being found guilty by a Rugby Football League tribunal of breaching the rules.
However, they appealed against the decision and an RFL appeals tribunal halved the fine but increased the sanction to a points deduction.
The deduction means Salford drop back to the foot of the table, with London Broncos moving above them.
The sanction relates to the closing stages of their televised match against the Tigers at the Salford City Stadium when Reds prop forward Darrell Griffin and the player who was replacing him, Vic Mauro, both became involved in tackles while the club had 14 players on the field of play.
Salford successfully defended their line for the last three minutes and went on to win the game 34-30 and move off the bottom of the table.
In a statement, the RFL said: “The tribunal handed down the increased sanction after rejecting Salford’s appeal against the original fine of £10,000 imposed at a hearing on May 8.
“Salford were deemed to be in breach of operational rules B1.1 (general competition rules - laws of the game); B2:4 (match day operations manual (section D15 - interchange); and D1.8 (a) (serious or persistent breach of the RFL operational rules).’’
The RFL investigated the case after Castleford lodged a formal complaint, with chief executive Steve Gill claiming that three plays took place while the Reds had an extra man on the pitch.