The 'Glad You Came' band had accused Aguilera of refusing to speak to them prior to a performance on The Voice USA a few weeks ago.
"She's a total bitch! She might not be a bitch in real life but to us she was a bitch. She just sat there and didn't speak to us," Parker previously said of the 'Dirty' singer.
He has now admitted that it was inappropriate for The Wanted to publicly share their disapproval of Aguilera's behaviour.
"We shouldn't have said it, to be honest with you," Parker told TMZ.
He added of the alleged snub: "We just think manners cost nothing, you know what I mean?"
Aguilera has not yet responded to The Wanted's comments on her Twitter page.
Watch The Wanted's 'Glad You Came' music video below: