The Manawatu-Whanganui Regional Council says legal action was needed to ensure a solution is found to the odour problem at the district council's wastewater treatment plant.
In February this year, the regional council warned the Wanganui District Council it would take the action if it didn't stop the smell that has been plaguing the North Island city for months.
A spokesperson says it lodged an application for an enforcement order from the Environment Court on Friday.
The regional council's regulation manager says an order with the weight and authority of the court was necessary to ensure that the district council carried out plans for a long-term solution.
Nick Peet says the order ensures that the council does its planning and design for either a modified or new plant in a timeframe that shows some urgency, given the effects of the smell on the community.
However, Mr Peet says the regional council has been in talks with the district council and has gone to court with an agreed, rather than adversarial, approach.
Mr Peet says if the application to the Environment Court is accepted, the district council will need to provide a long-term strategy by 30 May.
Wanganui mayor Annette Main is expected to get an initial report from experts in about four weeks outlining the best long-term options for fixing the problem.
