Coach Warren Gatland says Wales have done nothing wrong after being warned by tournament organisers for using non-World Cup squad players in training.
World Rugby said "no deliberate breach was intended" but Wales contravened "the spirit" of the rules by inviting omitted players to training.
BBC Sport understands non-squad players trained against the Wales team - announced on Thursday - that will face England in Saturday's Group A game at Twickenham.
But Gatland said: "We haven't broken any rules. Apparently we have broken the 'spirit of the rules'. What that means we don't know."