Town hall planners will work to block Government plans to temporarily relax rules on building extensions to homes, the Local Government Association insisted.
The LGA, which represents more than 400 councils in England and Wales, warned the plans could result in "unsightly and out-of-place" developments.
The proposals, unveiled by the Government last month, would relax permitted developments rights - rules which detail what does and does not need planning permission - to allow property extensions of up to 8m, in a bid to encourage growth in the construction sector.
Ministers pledged to consult on the plans before implementing them.
But speaking to the Daily Mail, the LGA's Mike Jones said: "This policy potentially gives the green light to unsightly and out-of-place development without delivering a big enough boost to the construction industry to justify the potential damage.
"The planning process works to ensure development is suitable for a local area and doesn't unduly impact neighbours."
Planning minister Nick Boles said: "The planning system needs to strike a balance between the rights of the homeowner and their neighbours.
"Our proposals will make it easier for thousands of hard-working families to undertake home improvements to cater for a growing family. It will also help generate new business for local construction companies and small traders."