Bristol mayor Marvin Rees is refusing to attend a meeting to discuss the spending of £10,000 by the regional mayor, Dan Norris, on a bus advert.
The West of England Combined Authority have said the political campaign was “unlawful”.
A meeting is set to take place this morning, but has already been pushed back by an hour after already being postponed on Tuesday.
In a letter seen by the BBC, Mr Rees has described the proceedings as “improper” and will not be taking part.
The bus advert was removed from public view, which included a large image of Dan Norris and his dog.
At the time, Mr Norris defended himself saying mayors “are meant to be visible”.
The meeting is set to take place at 11am today.
