Manawatu - Wanganui Regional Council says it will issue Wanganui District Council with an enforcement order from the Environment Court if a smell from a wastewater treatment plant persists.
The district council had until Thursday to stop the odour.
Group manager of strategy and regulation Nic Peet said the regional council will check to see if the smell has stopped during the next couple of days.
If it has not, the Environment Court will be brought in to monitor a plan currently in place, which has been jointly agreed by both councils.
Two new aerators were installed this week and 20 tonnes of lime was dropped into the ponds on Friday.
Mr Peet said enforcement action won't put an immediate end to the problem, but will assure the public the regional council is doing all it can to fix it.
Whanganui mayor Annette Main says the district council is also doing everything it can to stop the smell coming from the treatment plant.
Ms Main hopes the latest efforts, as well as further lime drops and aerator installations next week, will help fix the problem.