Saracens have been deducted 35 points and fined £5.3 million for salary cap breaches, Premiership Rugby announced on Tuesday.
An independent disciplinary panel said Saracens failed to disclose player payments in each of the last three seasons.
A Premiership Rugby spokesperson said: "The salary cap is an important mechanism to ensure a level playing field for Premiership clubs and maintain a competitive, growing and financially sustainable league.
"Today's decision by the Independent Panel upholds both the principle of the salary cap and the charges brought following an extensive investigation by Premiership Rugby."
Saracens responded and announced they will launch an appeal against the sanction.
A club statement read: "Saracens Rugby Club is shocked and disappointed by these heavy-handed sanctions and will launch an appeal against all the disciplinary panel's findings.
"The club is pleased the panel acknowledged it did not deliberately attempt to breach the salary cap and steadfastly maintains that player co-investments do not constitute salary under the regulations. This view is supported by independent legal and professional experts.
"As previously stated, the club made administrative errors relating to the non-disclosure of some transactions to PRL and for this we apologise. We are pleased to confirm we now have a robust governance framework in place and this will be overseen by an external counsel to ensure the Club follows best practice.
"Furthermore, it is the club's belief that the panel's narrow interpretation of the regulations is detrimental to player welfare across the league and is damaging the development of elite level rugby in the UK."
Sources have told ESPN that Saracens players were told about the decision in the morning.
In the event of an appeal, the sanctions will be suspended pending the outcome of the review.
Saracens won the Premiership and European Cup last season, but the sanction will send them bottom of the table with -26 points.
The club would have finished 10th in the table had they received the same punishment last season.