Governing body World Rugby slapped Wales with an official warning for using players outside of their nominated 31-man party during a training session on Wednesday, although accepted “no deliberate breach was intended”.
Regulations state that players who did not make the final World Cup squad are forbidden from partaking in practice sessions.
World Rugby judged that Wales contravened the “spirit” of the rules, although Gatland, whose side face England at Twickenham tomorrow in a pivotal Pool A clash, was in no mood for conceding any ground.
“We haven’t broken any rules. According to World Rugby, we’ve broken the spirit of the rules, so I don’t know what that means,” said Gatland. “We haven’t done anything underhand, and I don’t know what we’ve done wrong.
“You’ve either got rules or no rules, so what does the spirit of the rules mean? It’s either in the rules or not.”
Gatland, whose side currently top Pool A after beating Uruguay 54-9 at the Millennium Stadium on Sunday, insists England’s decision to reshuffle their entire midfield for the showdown caught him off guard.
He added: “We were expecting they were going to go with the same 10, 12 and 13 so that threw us.”