Rotherham have been deducted three points for fielding an ineligible player, the Football League has announced.
The Millers were sanctioned last week after they played Derby defender Farrend Rawson in their 1-0 win over Brighton on Easter Monday despite his loan deal from Derby having expired.
A three-man disciplinary commission has upheld the charge and docked them three points with immediate effect.
That plunges Steve Evans' side deep into the Championship relegation mire as they are now just a point above Millwall, who occupy the final spot in the bottom three, and two better off than second-bottom Wigan.
A Football League statement read: "A Football Disciplinary Commission has ruled that Rotherham United are to be deducted three points, with immediate effect, for fielding an ineligible player [Farrend Rawson] in the club's Sky Bet Championship fixture with Brighton & Hove Albion on April 6.
"The Millers won the match 1-0 with Rawson playing for the full 90 minutes. Rotherham were also fined the sum of £30,000, half of which will be suspended until the end of the 2015-16 season. The club must also pay the costs of the hearing and The Football League.
"The club has until May 1 to lodge an appeal."
The Millers hired top QC Jim Sturman to fight the charge and have expressed their disappointment at the Football League's sanction, saying they will consider an appeal.
"Rotherham United FC are very disappointed by the decision to deduct three points for fielding a player who was ineligible purely because of an administrative error," a statement read. "It is our view that true sports fans want to see competitions settled on the pitch and not to have them affected by what happens in disciplinary proceedings.
"We await the reasoned judgement of the Football Disciplinary Commission and once we have received it we will issue our appeal after discussion with Jim Sturman QC. In the meantime we are confident that our team possesses the will and spirit to ensure that the points deduction is academic by securing our Championship status on the pitch.
"It would not be appropriate to make any further comment on this matter until after the appeal process has been concluded."
The deduction throws Millwall and Wigan a lifeline at the bottom of the Championship, though with a game in hand Steve Evans' men have some added breathing space.
The Millers could book their place in the second-tier for next season on Saturday if they beat Norwich and Millwall and Wigan lose to Derby and Wolves respectively.
The date for the South Yorkshire club to lodge an appeal is the day before campaign comes to an end, meaning that if they do challenge the League's decision, the final standings might not be settled until after the season has concluded.