Cardiff councillor John Dixon is facing a disciplinary hearing from the Public Services Ombudsman for Wales, for calling the Church of Scientology "stupid" on a Twitter post last year.
Dixon's controversial Twitter message read: "I didn't know the Scientologists had a church on Tottenham Court Road. Just hurried past in case the stupid rubs off."
The Church is an organisation that promotes the practice and promotion of Scientology, which is about the power of a person's spirit to clear itself of past painful experiences through self-knowledge and spiritual fulfilment.
A spokesman for the Scientology organisation said the complaint about Dixon's tweet was made by an individual Scientologist who was personally offended by the comments.
A spokeswoman for the Welsh public services watchdog said an investigation into the matter had found there was likely to have been a breach of the code of conduct that local authority members must follow.
Dixon argued that the remarks were made in a personal capacity rather than as a councillor. However, he sent the tweet on his 'CllrJohnDixon' Twitter account, which implies that it is officially connected to the council.