Federated Farmers says the proposed southern boundary for the new Auckland Council is bizarre and will fracture the community of Franklin.
A report on how the super-city will be structured and run next year was issued by the Auckland Governance Select Committee on Friday.
It recommends giving most of the land in Rodney District north of Waiwera including Leigh, Tawharanui and Te Arai, to Kaipara District Council.
A small part of Franklin land in the southeast will go to Waikato.
The southern boundary would run close to Waiuku and Pukekohe.
But Federated Farmers says that line cuts right through the community of Franklin.
Auckland vice-president Wendy Clark says Waiuku and Pukekohe risk being split down the middle as the towns continue to grow.
She also says the town of Tuakau has been left out to dry in a no-man's land.
Ms Clark says the Waikato River, further south, would make a much more natural boundary.
