The PUP has been accused of creating a production line of fraudulent complaints against Belfast City Council over its handling of the Union flag issue.
A war of words has broken out after Sinn Fein's Jim McVeigh accused the loyalist party of falsifying letters of complaint after the council voted to restrict the flying of the flag at the City Hall in December.
The PUP and DUP complained afterwards that the council had breached equality rules during the process and decision on the removal of the Union flag.
The PUP had encouraged people to download a letter from its party website and personalise it with their name, address and signature and then use it to express concerns about the equality impact assessment and also its validity.
The DUP also lodged a formal complaint on January 10.
However, Sinn Fein claimed that some of the 500 respondents from the PUP were "not aware" they had sent letters.
Mr McVeigh claimed more than a dozen people had been left "shocked and angry" that their names had been used, as they had not signed a complaint.
"The PUP had a production line of fraudulent complaints," Mr McVeigh said.
This, however, was strongly denied by East Belfast councillor and deputy PUP leader John Kyle.
"I think it is a bit rich for Sinn Fein to talk about fraudulent complaints," he said.
"I think it was clear that there was a huge negative response to the decision of taking down the flag.
"People have been angry and annoyed.
"I think that's a disgrace – there has been no fraudulent behaviour."
Mr Kyle described writing the letter as a non-violent way of expressing the anger and told the chamber he would "offer no apology".
Speaking afterwards, Mr Kyle again dismissed the claims as "complete nonsense".
But he admitted the possibility that some letters had been signed by others.
"There may well have been a few letters signed by individuals on behalf of others, possibly family members, but we are talking about a very small number in the context of several thousand which were signed in numerous community settings throughout east, north and west Belfast."