A method and corresponding system for controlling whether a UE is served by a relay base station, based on consideration of the maximum-supported MCS of the relay base station's associated UE-relay. The method could apply where the UE is already served by the relay base station, in which case the question could be whether the UE continues being served by the relay base station or rather hands over to another base station. Or the method could apply where the UE is not yet being served by the relay base station, in which case the question could be whether the UE should initially attach with or hand over to the relay base station. Further, the method could be carried out by the UE and/or by a base station or other network entity.