Hurstville and Kogarah councils will be amalgamated, while Rockdale will be combined with Botany Bay Council under changes announced by the state government.
The move to exclude Rockdale from a long mooted St George council was immediately attacked on the grounds it would break up the historic district and destroy a "community of interest".
A similar move a few years ago to combine St George and Botany Bay police local area commands was dumped after a community backlash.
Premier Mike Baird confirmed the number of councils in Sydney would be cut from 43 to 25.
In regional NSW, 20 new councils are proposed, which would bring the total number of regional councils down from 109 to 87.
Mr Baird said Improved infrastructure and services and stabilised rates would "make ratepayers the big winners".
Labor MP for Kogarah Chris Minns said he had been prepared to support a sensible amalgamation that united all of St George.
"Instead, we are left with a plan that will make (former Hurstville mayor) Con Hindi the most prominent and powerful local government politician in our area," he said.
"This proposal is abysmal and will go a long way to destroying the culture of St George.
"Amalgamating Kogarah and Hurstville councils is a proposal purpose built for the Liberal Party.
"It is a gerrymander plain and simple."
Mr Minns said Botany and Rockdale were "shocking fit" as residents in the two council areas had little if anything to do with one another.
"They don’t use the same beaches, visit the same shops or play in the same sporting competitions'" he said
"It is a council that will be divided forever and is destined to fail.
"This proposal needs to be met with resistance from local ratepayers.
"Either pursue a combined St George, or let each council stand alone."
Labor member of Hurstville Council Brent Thomas said Local Government Minister Paul Toole had listened to Cr Hindi, and the result was a gerrymander for the benefit of the Liberal Party in St George.
Asked by the Leader about the break-up of the St George councils, Mr Baird said he didn't want to discuss the details in each area, but residents would have an opportunity to have their say.
Detailed merger proposals are being finalised and will be referred to the chief executive of the Office of Local Government for examination and report under the existing process set out in the Local Government Act.
The chief executive will appoint delegates, who will commence a public consultation process for all 35 proposals, including public hearings.
Following this stage, final proposals will be referred to the Boundaries Commission for comment.
Through the Stronger Communities Fund, every new council that is established will be provided with up to $15 million to invest in community infrastructure.
Each new council will receive funding of up to $10 million to ensure ratepayers do not bear the upfront costs of merging.
Mr Toole said under the proposal there will be no change to merged council’s existing rate paths for four years.
The public consultation process will commence in January, once detailed proposals are made available at www.councilboundaryreview.nsw.gov.au
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