Local Government New Zealand (LGNZ) is criticising a super-city proposal which it says would give control of three-quarters of Auckland's most valuable assets to unelected powers.
It believes democracy would be threatened by handing over billions of dollars worth of services, such as water and transport, to government-appointed Council Controlled Organisations (CCOs).
CCOs already provide land, infrastructure and property services for about half of all local councils. But LGNZ says those councils have a maximum of 25% of their assets controlled in this way, while 75% is proposed for Auckland.
In an open letter to mayors, president Lawrence Yule says handing over the majority of assets to unelected CCOs is unfathomable.
Mr Yule told Morning Report that CCOs should not be in control of core council activities and ratepayers need to make sure they hold the new Auckland Council accountable.
However, the Council for Infrastructure Development says under legislation before Parliament the super-city council would retain control, with the power to fire members if it was unhappy with their performance.
Listen to Morning Report interview with Lawrence Yule
CCOs will be accountable - Hide
Local Government Minister Rodney Hide on Tuesday dismissed criticism of plans to control many of the super-city's assets.
The minister told Morning Report CCOs already operate successfully in Auckland, saying the super-city will expand on the model. He says it will be accountable to the Auckland Council and ratepayers.
Mr Hide says all of the operations could have been made government departments, but that would have meant no transparency or accountability.
Listen to Morning Report interview with Rodney Hide