London Welsh have been fined 10,000 euros for fielding ineligible scrum-half Tyson Keats in the Amlin Challenge Cup last season.
Keats was not registered properly for the competition when he faced Stade Francais on October 13 last year.
The punishment comes on top of the five-point penalty and £15,000 meted out by the Rugby Football Union in March after Keats played in 10 Aviva Premiership games when he was ineligible.
Former team manager Mike Scott was banned for life from rugby for his role in supplying false information about New Zealander Keats, including sending a false passport to the RFU.
An ERC statement read: "London Welsh have been fined 10,000 euros by an independent Disciplinary Committee on foot of a misconduct complaint brought against the club by ERC.
"The misconduct complaint was that London Welsh selected Tyson Keats for the Amlin Challenge Cup round one match against Stade Francais Paris on 13 October 2012 when Keats was not properly registered with ERC as a member of the club's tournament squad, and was therefore an ineligible player.
"ERC awaited the conclusion of a Rugby Football Union (RFU) disciplinary hearing involving London Welsh, as well as London Welsh's subsequent appeal against the RFU decision, before beginning its own investigation into Keats' registration for the 2012/13 Amlin Challenge Cup.
"After considering written submissions, the independent Disciplinary Committee determined that London Welsh were guilty of misconduct in that they had breached the Amlin Challenge Cup player registration rules."