Three district councils have opposed a bid by Wiltshire County Council to become a unitary authority.
The county council should have a decision on their bid by March
West Wiltshire District Council accused the county authority of "promoting its own interests in a bid for power".
Kennet and Salisbury District Councils have also opposed the move. North Wiltshire District Council has signalled its approval for the bid.
The county council said it believed one council for Wiltshire would offer better services and strong leadership.
But the leader of West Wiltshire District Council, Sarah Content, said: "The last thing we need is a major reorganisation and distraction.
"All that would do is cause a deterioration in services for several years, cost millions to achieve, and result in a remote bureaucratic machine.
"There is a misconception that a unitary council is inevitable. This is certainly not the case especially in parts of the country, like Wiltshire, where it doesn't make sense."
Chief Executive Andrew Pate said they had spotted "major flaws" in the county's proposal.
In a letter to the government, Ms Content said: "The view of this council, and also our colleagues in Kennet and Salisbury, is that any single authority would be too large geographically and would become centralist, unwieldy and unpopular."
She added the bid contained little information about how community identity would be protected and that the proposed reduction in the number of local councillors would weaken the links with local people.
Devizes MP Michael Ancram said: "The bigger the local government unit the remoter and less accessible it becomes.
"Once again bigger will not be more beautiful or more efficient. It will be less accountable, less balanced and ultimately less democratic."
County Council leader Jane Scott said: "We really believe one council for Wiltshire is the right way forward for local people.
"It will provide better services that are value for money, an increase in local decision making and stronger leadership," she said.
Ms Scott said the council will be cheaper to run and will provide one point of contact for customers' enquiries.
The county council is awaiting government approval for its bid.