Critics say revamp proposal could reduce districts' voices at regional council table.
Waikato mayors are opposing a regional council proposal to change the region's boundaries.
The mayors say it is an unnecessary expense and that some districts could lose their voices.
The regional authority is proposing to reduce the number of constituencies from eight to six in a move it says groups together community interests such as coastal, farming and urban.
The number of general councillors would remain at 12 but two new Maori seats would be introduced in the north and south of the region.
The biggest changes would be merging South Waikato and Matamata Piako with part of Hauraki into a new ward called Waihou. Rotorua, which is now part of South Waikato ward, would be combined with Taupo.
Hamilton has the smallest land area but the biggest population, and remains unchanged with four seats.
The most affected councils - Matamata-Piako and South Waikato district - are strongly opposed to the proposal which they say could reduce their representation at the regional council table.
South Waikato mayor Neil Sinclair said the regional council had treated with "disdain" a letter signed by all the Waikato district mayors calling on the regional council to retain the current structure, and had ignored their views.
"It's another indication of the regional council deciding what goes on and to hell with what goes on with the other mayors.
"I don't think there's been a case where all the other rural mayors have made a case to regional council and been ignored like that. I believe there's a very great likelihood South Waikato will lose its voice at the regional table and I find that distressing."
Matamata-Piako mayor Hugh Vercoe supported the status quo, under which one regional councillor represented Matamata-Piako and another represented South Waikato.
"Each local authority would like to have a regional councillor representing their area. When you go to a combined one ... you could get two people living in Matamata who represent the whole area because that's where the population is."
Mr Vercoe said that could leave a district without any representation. But Waikato Regional Council electoral officer Maureen Poole said constituencies needed to fairly represent the region's entire population and South Waikato-Rotorua on its own did not comply.
South Waikato-Rotorua's population size also fell outside the threshold, determined on population size, when the last review was done, in 2006, but it was given special exemption from the Local Government Commission.
Ms Poole said the population changes in South-Waikato constituency meant there was "an even bigger discrepancy", and this was exacerbated by the fact a large number of constituents in South Waikato and Rotorua would be transferred to the Maori south constituency.
Under the proposal, the North Waikato and Central Waikato wards will also merge into a Waikato ward, with the number of seats falling from three to two. But Waipa-King Country has inherited part of the central Waikato area and with it another seat.
Submissions on the proposal close on July 18 and the final structure will be introduced at the next election in October next year.