The Imlay meatworks could face prosecution as it continues to create a stink around its Heads Rd operation.
With the works' odour problems unabated, Horizons Regional Council has started a formal investigation that could lead to prosecution.
In the past week there have been more complaints of offensive smells to Horizons' pollution line - 0508 800 800. In the previous two months the meatworks owner, Affco, has been fined four times for a total of $5400.
Compliance staff rostered in Wanganui are now keeping record of the odours.
Horizons strategy and regulation manager Nic Peet said another aspect of the investigation would be formal interviews with Imlay staff, asking about the cause of the problem and what they had done to fix it.
Horizons staff are also talking to people affected by the odour.
"Because they're continuing to breach the abatement notice, the next step is a formal investigation with a view that we may need to then take further regulatory action that could include a prosecution. But clearly I don't want to prejudge anything at this stage," Dr Peet said.
He knew the process was frustrating to the public because people could not see anything happening.
Imlay plant manager Troy Lambly would not say how many complaints it was getting on its own odour line - 06 3492435.
He had been to see one complainant, Jane Motu, who said he explained the situation clearly and it would be better soon if what he told her worked.
She would not pass on his explanation, saying it was confidential.
Mr Lambly was also asked to pass it on to Chronicle readers, but would not.
"We've decided we will address things directly with our complainants," he said.