First-term councillor Karen Arnold yesterday issued proceedings in the Wellington High Court. She claims Mr Shadbolt defamed her in a series of columns in The Southland Times between October 2014 and April 2015.
Ms Arnold said it was clear her willingness to challenge council consultation and decision-making processes had put her offside with the city's powerbrokers.
"That includes the mayor, who has used the privilege of a fortnightly column in The Southland Times to make his displeasure clear."
"It is with considerable reluctance that I have issued these proceedings, but I cannot leave Mr Shadbolt's attack on my reputation to remain unchallenged. I am also conscious that Mr Shadbolt has threatened to sue me if I took action against him."
Fairfax Media - Ms Arnold's former employer - is also named as a defendant in the claim.
Ms Arnold is a former journalist who worked for The Southland Times and the Sunday Star-Times.
She was elected to the Invercargill City Council in October 2013, and was the second highest polling candidate.
She has instructed defamation specialists Peter McKnight and Ali Romanos to act for her in relation to the proceeding.
Mr Shadbolt became the longest serving city mayor in New Zealand's history in 2013 - when he was reinstated a seventh time in Invercargill by 12,000 votes.
