Salford have been docked two competition points for having 14 players on the pitch during their Super League win over Castleford in April.
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 today 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 on April 27 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.
Warrington's former England coach Tony Smith publicly slammed the RFL after the initial hearing for failing to dock Salford points.
"I would hate to have lost that game because our opponents had an extra man out there," Smith said.
"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."
Such cases have been rare over the years. In 2006 St Helens were charged with misconduct after a similar incident against Hull and were fined £100.
However, in Australia in 2009, Canterbury Bulldogs forfeited winning points against Penrith for fielding 14 players during their 28-26 victory.