Mr Prendergast has been accused of striking Labour colleague Chris Newby twice. Mr Newby declined to lodge an official complaint, but did write a letter about the incident to Labour Party headquarters in London.
Mr Newby confirmed he had written the letter but said: 'I'm making absolutely no comment. I'm unhappy that this has got into the public domain. This is about a private, internal Labour Party matter.'
Labour local government officer Abigail Melville confirmed that party general secretary Tom Sawyer had received a letter about the incident, which she said was claimed to have taken place at a Christmas party. Ms Melville added:
Mr Prendergast was unavailable for comment.