Having to wear the suit to and from training was punishment for being just seconds late for a team meeting. Fines and punishments are doled out by Irish rugby's "sheriffs", James Ryan, Jack Conan and Dave Kilcoyne.
"There's a bit of a dictatorship going on in camp at the moment," explained Beirne.
"We have three lads that call themselves the sheriffs. They are in charge of any misdemeanours or any fines that need to take place within camp.
"Unfortunately I turned up a couple of seconds late for a meeting and they decided to fine me. I had to spin the wheel of fortune and I landed on number ones to and from training, hence the suit.
"But, it fell on me today so everyone gets to see me in a nice suit, so how bad?"
Beirne said he wasn't "at liberty" to disclose what other punishments were dispensed.
"One of the worst ones is I think there’s a silent one-minute dance which is actually probably punishment for everyone sitting in the room as well as it is for the man who has to do it," he said.
"There’s a wheel back in the camp they have all different punishments on it. So it could land on whatever.
"James Ryan, Jack Conan and Dave Kilcoyne [are the three sheriffs]. The reason it’s a dictatorship is because they are claiming they’re above the law. So there could be a French revolution yet.
"The power’s definitely going to their heads, particularly Dave Kilcoyne. He’s enjoying it a bit too much for people’s liking I think."
Ireland face Tonga at 8pm on Saturday evening.
"They're a serious side when you look at the team on paper," said Beirne.
"I have no doubt that they are going to have a go at us. They'll certainly attack out wide and then take us on up front as well. We've got to be ready for that.
"Looking back at the Samoa game, we were quite off it, we felt. A lot of mistakes, we were disappointed with how our set piece went. Tonga are probably going to look at those areas and come after us in those areas.
"We are going to have to improve massively on those from the weekend just gone. We're still not happy with where we are there, particularly lineout. We're putting pressure on ourselves to improve that area, for sure."