He's got a point. It has happened - New Zealand teams on this tour have tried to protect the catcher taking the high ball, or held their line a little too fiercely when the ball has been put in behind them and Lions players are trying to get after it.
So now of course Peyper and his match officials on Saturday night are going to be looking for it and already they are under pressure to find it. They will be under even more pressure to penalise it especially when the thousands of Lions fans call for it every time an All Black makes a successful catch.
But as much as it was an astute move by Gatland to bring up his concerns about blocking, so too was it a risk. The All Blacks will be wary of giving Peyper any reason to penalise them for blocking and they know they don't need to do it.
Their aerial game hasn't relied on it before and shouldn't need to now.
The bigger concern for Gatland is that he has raised the stakes because if he wants referees to go looking into micro details then it's best only to do that from a position of absolute purity.
The Lions can't pretend they are squeaky clean on this front. They run plenty of interference themselves - look what happened to Nehe Milner-Skudder after he kicked through for Liam Messam's try for the Maori in Rotorua.
He's blocked by the retreating defence. Then there is this whole business of the Lions linesepeed.
Defence coach Andy Farrell says his troops spring into action on the b of the bang. Which is mostly true. But it's not when they charge that is the issue, it is from where. He can't see it because he's the Lions defence coach, but all tour the Lions have set their defensive line in front of the hind feet.
Maybe by just a quarter metre, sometimes a half but enough to make their defence more effective.
The Lions have also been fortunate to avoid more yellow cards for high tackles. Dan Biggar was lucky to escape one in Hamilton and CJ Stander should have had at least 10 minutes in the bin against the Blues for taking Steven Luatua around the chin.
The All Blacks will possible make these very points to Peyper privately ahead of the game. But maybe they won't bother because usually it is best to simply trust the referee to do his job and not heap too much pressure on him.
Ask him to look too hard at one thing and he'll miss plenty of others. And besides teams that worry too much about what their opponents are supposedly getting away with are probably not focusing enough on their own game.
