The Exiles were handed a five-point penalty and a £15,000 fine by the Rugby Football Union in March for fielding Keats in 10 Premiership games when he was ineligible. A further suspended five-point penalty was later removed after an appeal.
Mike Scott, the former London Welsh team manager, was banned for life from rugby over his role in the matter after he admitted supplying false information regarding New Zealander Keats, including a forged passport, to the RFU.
Following the deduction, Welsh finished bottom of the Premiership and Newcastle's Championship triumph effectively confirmed their relegation.
But, as Keats also featured for the club in the Amlin Challenge Cup, ERC has decided Welsh have a case to answer over his registration for European competition.
The complaint, which is being dealt with on the basis of written submissions, will be considered by an independent disciplinary committee chaired by Antony Davies of England.
ERC's statement read: "Following an investigation by ERC disciplinary officer, Roger O'Connor, into the registration of the London Welsh player, Tyson Keats, for the 2012/13 Amlin Challenge Cup, a misconduct complaint has been made against London Welsh.
"The complaint is that London Welsh may have committed one or more acts of misconduct when the club's then team manager, Mike Scott, registered Keats for the tournament."
- Sports & Recreation