A frustrated Sydney coach John Longmire wants some "serious consequences" if it is proven an interchange infringement was incorrectly paid in the Swans' loss to Carlton at the SCG on Friday night.

The AFL have already confirmed an investigation will take place into the incident, where a 50 metre penalty was called against Sydney because they had 19 players on the ground deep into the third quarter.

Carlton's Setanta O'hAilpin then kicked a goal from in front to extend their lead to seven points as the Blues rallied for a 12.15 (87) to 10.11 (71) victory.

Adam Goodes and Dan Hannebery were the players in question and there was confusion as they appeared to be uncertain about coming on or off the ground.

Longmire felt his side had done nothing wrong and was keen to know what penalty would be imposed if it was determined the officials had made an error.

"They kicked a goal that got them back to seven points," Longmire said.

"If we make a mistake and put an extra player on the ground, it's a 50 metre penalty and a goal.

"That's pretty clear.

"If they've made a mistake and it's confirmed they've made a mistake, what happens?

"Is it just a mistake and we move on?

"I think someone has to look at it. If that's a pretty basic mistake, and I'm only assuming it was, but if it was and it was pretty basic and not difficult, do we just move on and say it was a mistake at a pretty important part of the game?

"I think there has to be some pretty serious consequences to it if it's proven."

At the conclusion of Carlton's press conference, an AFL spokesman immediately got on the front foot, informing the media an investigation would be carried out, but they were confident the right decision had been made.

"There will be an investigation during the week about the decision on the interchange infringement," the spokesman said.

"The free kick was paid for 19 on the field and at this stage they're fairly confident in the decision."

Longmire felt it should be pretty straightforward for a mistake to be quickly rectified during the game.

"I would assume there was a fair delay that if there was a mistake it could've been rectified straight away.

"I'm sure there was time to count the numbers on the bench.

"I might issue my own please explain"

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