A group that helped sway Hamilton City Council to stop fluoridating its water is now taking aim at Auckland, Wellington and other centres.
The 7-1 vote this week by Hamilton councillors has sparked calls for health officials to take a more hands-on approach to the issue, and the Ministry of Health says it will review its options next week.
Twenty-two of New Zealand's 67 councils add fluoride to their drinking water supplies, and officials see it as a safe and cost-effective way to reduce tooth decay, particularly in low socio-economic groups.
But opponents such as the Fluoride Action Network New Zealand say fluoridation is "mass medication" with a chemical they claim is harmful and is linked to arthritis and cancer.
The group is targeting the Whakatane and Hastings councils, which are holding fluoridation referendums with local body elections this year, as well as larger councils such as Wellington and Auckland.
By the end of this month, Hamilton will become the second largest city to go without fluoridation.
Mary Byrne, national co-ordinator for the Fluoride Action Network NZ, said there were growing efforts to lobby Auckland Council, while her personal focus would be on Wellington City Council.
But a Wellington City Council spokesman said there were no plans to change its policy.
The Auckland Council is to prepare a water strategic action plan that will look at a range of issues relating to the region's water supply over the next 20 to 30 years.
Health authorities have reacted with dismay and concern to Hamilton's decision.
"The current problem is we have clear guidelines and statements from the Ministry of Health, but the decisions are left up to local councils, and the local councils can be easily influenced," said the president of the New Zealand Dental Association's Otago branch, Dr Jonathan Broadbent.
The Ministry of Health and district health boards could only offer advice and expertise on fluoridation - and Dr Broadbent said he wanted to see their policy put into practice.
"For every dollar spent on water fluoridation, 38 dollars are saved in un-needed dental treatment."
Labour's health spokeswoman Annette King said she had tried to find a better approach to fluoridation in a forum she organised as health Minister in the early 2000s.
She believed it was now time to review who should make decisions on fluoride - powers that Local Government New Zealand also says should never have been given to councils.
Even Hamilton Mayor Julie Hardaker, who tabled the motion to remove fluoride, said the issue was a public health matter that the government needed to determine, and her council would write to Health Minister Tony Ryall.
Mr Ryall's office referred comment to Associate Minister Tariana Turia's office, which in turned referred comment to the ministry.
The ministry's chief adviser on child and youth health, Pat Tuohy, believed it was legitimate for councils to make their own decisions if they were acceptable and fell within their power. He said the establishment of a new advocacy group would be considered when the issue is discussed next week.
Fluoride in New Zealand
Who's got it
Auckland, Wellington, Masterton, Lower Hutt, Upper Hutt, Taupo, Gisborne, Whakatane, Hastings, Palmerston North, Dunedin and Invercargill. Whakatane and Hastings are holding referendums this year.
Who hasn't got it
Christchurch, Whangarei, Tauranga, Rotorua, Napier, Wanganui, Nelson, Timaru and Greymouth have never fluoridated their water. New Plymouth, and now Hamilton, decided to stop doing so.