Local Government New Zealand is concerned about the pace with which the Auckland governance reforms is being carried out.
Friday was the final day of hearings by a Parliamentary select committee which spent three weeks looking at the merging of eight councils in Auckland into one.
A new combined council will come into being in October 2010.
Local Government NZ president Lawrence Yule told the committee that what happens in Auckland is of fundamental relevance to all of New Zealand.
He said the pace of the changes may undermine the sustainability of the reforms, and diminish the country's future economic development.
The committee will report back to Parliament by 4 September.