The Meat Workers Union says an Employment Court decision will ensure that senior meatworkers at four AFFCO plants will continue to be rewarded for loyal service.
In January, AFFCO laid off some seasonal workers at four of its North Island processing plants.
New employees were kept on ahead of those with years of loyal service.
On Wednesday, the Employment Court ruled that AFFCO was required to employ and lay off seasonal workers in accordance with their initial start date.
Meat Workers Union national secretary, Dave Eastlake, says keeping those that had only worked a few weeks at the four North Island plants ahead of long-serving workers went against collective agreements.
Mr Eastlake says the decision affects hundreds of meatworkers at the four AFFCO plants.
The union will seek wages for those workers who were wrongly laid off, he says.
AFFCO chief executive Hamish Simson says the court's decision recognises union members seniority but also acknowledges individual employment contracts.
He said the ruling has also said that rights assoicated with a start date at a company apply whether the employee is a union member or not.
Mr Simson says that aspect may not have been considered by the union in the past.