Two council leaders are joining forces to fight a scheme which would see fluoride added to water supplies in Southampton and parts of Hampshire.
NHS chiefs agreed the move in 2009 but Public Health England (PHE) and Southern Water have yet to finalise details of the scheme.
PHE said it was still committed to a 2014 date to start fluoridation.
But Hampshire and Southampton council leaders believe new legislation may give them power to scrap the plan.
The South Central Strategic Health Authority (SHA) agreed to a request by Southampton City Primary Care Trust in 2009 to add fluoride to tap water for about 200,000 people, claiming it would be beneficial for children’s health.
But the SHA was scrapped and its duties taken over by PHE on 1 April.
Simon Letts, leader of Southampton City Council, said no contract was signed between Southern Water and PHE when the new body took over.
He argues that as a result the scheme may not be classed as “existing” and, under new legislation, only councils have the power to decide on new fluoridation projects.
He said: “I am organising a meeting with the leader of Hampshire County Council to come up with a way forward.
“We will look at what we can do with as little cost to the public as possible. The council would probably vote against it [fluoridation] and we will also consider a referendum.”
Hampshire leader Roy Perry believes it is “impossible” to ensure only the homes in the consultation area get fluoride and possible legal concerns could be delaying the implementation.
He said: “We think it is wrong to put medication in our supply. It is impossible to add fluoride and guarantee where it will go.
“I’m happy to meet up with [Mr Letts]. There is no doubt local public opinion is opposed to it.”
Meanwhile, confusion remains as to what stage the scheme is currently at.
The health body said it was still waiting for a final feasibility study from Southern Water, but the water company said the report “is in their [PHE’s] hands”
A PHE spokeswoman added: “[We] are not aware of having received and accepted a final, completed report.”
Stephen Peckham, from Hampshire Against Fluoridation which is concerned about possible adverse health effects said: “The whole situation is causing confusion.”
Sept 2008 – Southampton City Primary Care Trust calls for fluoride to be added to water and public consultation run by South Central Strategic Health Authority (SHA) starts
Nov 2008 – Southampton City Council votes to back the plan, Hampshire County Council votes to reject the scheme
Feb 2009 – Results of consultation show 72% of 10,000 respondents oppose the move
Feb 2009 – SHA approves the scheme
Feb 2011 – High Court legal challenge by resident Geraldine Milner fails
April 2013 – Public Health England take over scheme from the disbanded SHA and vows to press ahead