"This is both remiss and negligent of council to put forward an option into the 10-year plan without, at very least, a feasibility study to assure residents it is possible, let alone preferable."
It would be the loss of one of the few council services specifically for Mangaweka people.
The draft long-term plan listed the proposal as the council's preferred option.
"It's more than a flagging ... it's actually a plan," Ms Brannigan said.
Councillor Lynne Sheridan said the proposal "seems to have gone down like a bad pill".
Ms Brannigan said many in the community would be interested in being part of a residents' working group to discuss the future of the town's wastewater.
"Mangaweka is a very active, dynamic community and when we need to come together we are quite good at that stuff."