The leader of the Scottish Liberal Democrats has described SNP plans to reduce the number of local authorities across Scotland to just six as "extreme".
Alex Cole-Hamilton told the Record the country did not need more council areas so large they could be seen from space.
Highland Council cited as cautionary tale
Speaking ahead of his party's conference in Edinburgh this weekend, the MSP pointed to the example of Highland Council as a local authority so large it was effectively unmanageable.
The SNP Government rushed out proposals last month to replace Scotland's current system of 32 local authorities with between six and eight new regional councils.
There are also plans to create more than 100 community authorities, but it is not expected these bodies would have much in the way of powers.
Consultation timeframe dismissed
SNP ministers have said a three-month consultation, due to end before Christmas, should be enough time to reach agreement - a claim dismissed by the Lib Dem leader.
Cole-Hamilton disagreed when asked if he thought the Borders should be merged with the Lothians to forge a new council area, or whether East Renfrewshire should be joined with Glasgow.
"I would point to Highland Council as a cautionary tale. We've long advocated reforming it as it's not fit for purpose. It's vast - you can see it from space," he said.
"Most Highland councillors come from metropolitan areas like Inverness or Fort William, despite the geography of the area being very rural. It means the decision-making is focused on urban conversations, and not on access to services in somewhere like Caithness.
"I think that's a salutary lesson for local government reorganisation. You shouldn't imagine that regionalisation is going to make anything better on the ground."
Doubts over SNP seriousness
He added: "I think the SNP Government are at sea on what this actually means. We've had two ministers last week saying different things on whether these regional authorities will have more powers.
"So I'm not entirely sure the SNP are serious about this. I think they've reached for the most extreme model of local government reorganisation to begin the conversation.
"We'll engage with any discussion about reform - but we're not convinced."
Cole-Hamilton continued: "Lib Dems are reformers. It's in our DNA. We believe nothing should be set in aspic.
"We think power and decision making should be as close to people as it can possibly be. And we should always keep that under review.
"We'll move forward with this programme in good faith. On local government reform, we'll produce our own set of proposals, which are not about centralisation, but a much more rational approach to local government."
Health board cuts also questioned
Swinney has also revealed plans to cut the number of NHS health boards from 14 to just two - another proposal met by scepticism by the Lib Dems.
Asked how many health boards there should be in Scotland, Cole-Hamilton said: "I don't know what the right number is, but for me the litmus test is, does it make the delivery of health and social care better for people on the ground?
"I don't think that taking decision-making into two massive health boards will lead to that.
"And I don't think people out there in communities really care about the number of health boards. They just want to know when they'll get their hip replacement."
