An application has been made for a judicial review of the Hamilton City Council's decision to resume fluoridating its water.
The group Safe Water Alternative New Zealand (Swanz) has lodged a statement of claim in the High Court in Hamilton.
It's based around the council's process and a claim by the group the council failed to comply with the special consultative procedure in the Local Government Act.
It also claims the supply of the chemical added to the water to create fluoride (hydrofluosilicic acid) is unlawful, as it is a medicine.
The council says it will defend the court action.
The group, Swanz, is also seeking an interim court order preventing the council resuming fluoridation until the case is heard.
Co-ordinator Trevor Crosbie said the council had breached the Local Government Act and further consultation should have happened before voting to reintroduce fluoride. He said he would be speaking with his lawyer in the next few days.
Fluoride Action Network spokesperson Mary Byrne supports a judicial review. She said people are uneducated about the dangers of fluoride and the councillors had not done their job in informing people about all the facts.
The Waikato District Health Board has previously spent about $47,000 on a pro-fluoride campaign - $8000 of it on billboards and banners.
The DHB communications director Mary Ann Gill has said it was unfortunate the DHB had had to spend so much time and effort on the referendum when there were other major challenges.
These included "the return of diseases such as measles, whooping cough and hepatitis B, which should have been eradicated in my lifetime with the benefit of immunisation."
Ms Gill has predicted that a judicial review would mean more taxpayer money would have to be spent.