Lib Dem, Tory and Green candidates for the parliamentary seats in Southampton have said they opposed plans to add fluoride to the city's tap water.
The South Central Strategic Health Authority (SHA) agreed the plans in February 2009.
The decision was made despite 72% of 10,000 respondents in a public consultation opposing the move.
The plan is the subject of a judicial review after a private legal challenge. Labour has not commented.
Resident Geraldine Milner has mounted the legal challenge against the decision by the SHA.
The judicial review will be based on government policy, which states most residents need to be in favour of the move.
Campaign group Hampshire Against Fluoridation and other supporters delivered a petition with 14,000 signatures to Downing Street on 9 June last year.
Councillors have also called on the SHA to hold a referendum, but the authority said it "has no mechanism" to do so.
The health authority argued that mass fluoridation was a "safe way" of tackling tooth decay and said it was confident the decision was "in the best interests of the health of local people".
John Spottiswoode said he was standing as Green Party candidate for Southampton Itchen in an attempt "to remove MPs and councillors who support water fluoridation".
He said: "Seventy-two per cent rejected water fluoridation in the public consultation.
"It is also deeply unethical to force people to drink a known toxin via their water supply, especially if it is being used to medicate people against their will."
Chris Bluemel, also from the Green Party, said: "A judicial review into the policy is currently pending in the High Court, and I await the outcome of this with interest. Regardless of the outcome, I will remain opposed, and will continue to call on the Strategic Health Authority to reconsider its position."
Sandra Gidley, Liberal Democrat MP for Romsey and prospective parliamentary candidate for Romsey and Southampton North - created by boundary changes - said: "The issue is not whether fluoridation is a good or bad thing.
"It is more about the sham consultation by the SHA and the expressed wish of the public being ignored."
David Goodall, Lib Dem candidate for Southampton Itchen, has actively campaigned against the decision.
He said: "If elected I will use my position to lobby the health minister to change the plan."
Royston Smith, Conservative candidate for the Southampton Itchen constituency, said: "I wouldn't argue with the science but I don't believe people should have a medical product put into their water supply unless and until they have been fully consulted and have had their chance - through a referendum if necessary - to endorse or otherwise the decision."
And Caroline Nokes, Conservative candidate for Romsey and Southampton North, said: "The fact that the SHA decided to ignore the vast majority of views expressed in the consultation, did not even bother to consult some of those residents who will be affected, and is certainly not accountable to any elected body speaks volumes.
"The consultation process was a sham.
"I fully support the judicial review process, believe there should be a referendum on this matter and the results of that should be binding."
The candidates standing for election so far in the Southampton Test constituency are: Alan Whitehead, Labour; Jeremy Moulton, Conservatives; David Callaghan, Lib Dems and Chris Bluemel, Green Party.
The candidates standing for election so far in the Southampton Itchen constituency are: John Denham, Labour; Royston Smith, Conservatives; David Goodall, Lib Dems; John Spottiswoode, Green Party and Tim Cutter, Trade Unionist & Socialist.
The candidates standing for election so far in Romsey and Southampton North are: Sandra Gidley, Lib Dems; Aktar Beg, Labour and Caroline Nokes, Conservatives.