John Shewell dubbed The Argus a 'rag' on Twitter, when he complained the newspaper had reported that the council was thinking of introducing a 'tourist tax'.
Subsequently, Argus editor Michael Beard emailed She-well, threatening legal action.
Beard wrote: 'As to your comment describing The Argus as a "local rag", the advice from our company lawyer is that the tweet as a whole is defamatory, in that it characterises The Argus (and therefore the editor and individual members of staff) as a "rag" that carelessly or incompetently publishes false or misleading information and is not to be relied on.
'Our concern is that you have spread false and insulting information about The Argus, apparently designed to discredit us and our staff. I am taking advice on how to protect our employees from these unjustified attacks.'
Beard also complained that the news story did not claim the council was considering introducing a tourist tax. The email was leaked by former Brighton & Hove social media consultant Michael Taggart.
Shewell was not available for comment as PRWeek went to press.