Local Government New Zealand and the Dental Association say the decision on whether or not to fluoridate water supplies should never be left to local councils.
Hamilton City Council on Wednesday voted 7-1 to stop putting fluoride in its water supply once supplies run out later in June.
The council is, however, writing to the Health Minister to say it should not have been responsible for making the decision.
Whangarei, Tauranga, Rotorua, Napier, Whanganui, Nelson, Timaru and Greymouth have never fluoridated their water, while New Plymouth recently decided to stop the practice.
The Ministry of Health supports fluoridation as a way of protecting teeth from decay, but says the decision is for councils to make because they represent communities.
The ministry's chief adviser on child and youth health, Pat Tuohy, is, however, worried that councils are being subjected to scare tactics.
"I think that there is a global, very strong advocacy to remove added fluoride from water from a range of people who have very strong feelings about it and I think they're very well organised and use what I would call scare tactics to scare councils into making this decision."
Local Government New Zealand says councils should never have been given the power to choose whether to fluoridate their water.
Many councils are due to vote on the topic or hold binding referendums on it as part of this year's local body elections.
Hastings is one of the regions putting the matter to a vote. The city's mayor and Local Government New Zealand president Lawrence Yule is against councils having the power to choose whether to fluoridate water, but says his hands are tied.
"If their communities say they want (fluoride) out then the local authority has the ability to take it out. Now the Government may not like that but they've given that right to the local authority.
"If the Government had a different view and thought it was so important like they've just done with folic acid in bread, then they should step into that place."
The Dental Association says the decision should lie with the Ministry of Health or district health boards, which have access to the best scientific information.
Association president Geoff Lingard says it is very difficult for local councils to make such public health decisions.
Ministry of Health figures show just on half of all New Zealanders drink fluoridated water.