The Free Speech Coalition has filed legal action against the Auckland Council and its mayor, Phil Goff.
The proceedings come after Mr Goff's clear message that far-right advocates Lauren Southern and Stefan Molyneux should not be speaking at council venue the Bruce Mason Centre.
The speakers are best known for the contentious views on topics including gender, feminism, immigration and Islam.
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The pair's event was cancelled by venue operator Auckland Live, which cited health and safety reasons.
Free Speech Coalition member David Cumin says they presented Mr Goff with an open letter suggesting he avoid litigation costs by reopening discussions with event promoters over the potential hosting of Ms Southern and Mr Molyneux.
Dr Cumin told RadioLIVE Drive that the action is to ensure politicians and officials don't discriminate against views they dislike.
In an earlier statement, he said: "Mr Goff now claims it wasn't about banning the speakers because of their political views, but about safety.
"What he risks is delivering a 'heckler's veto', where potential protesters get to decide who Aucklanders can hear from or associate with."
Auckland Council told Newshub its legal team is assessing the claims, but is unable to comment further as the matter is before the courts.
Ms Southern was originally denied access to Australia, but her visa was approved by the Home Affairs Department last week.
She told Sky News Australia the initial visa denial was due to her criticisms of Islam.
Listen to the full interview with Dr David Cumin above.