Weight had been including stuffing and marinade.
Chicken producers Ingham and Tegel have been warned for including stuffing and marinade in the labelled weight of their chooks.
The Commerce Commission issued both companies with warning letters and said their labels were likely to be misleading customers.
Commissioner Anna Rawlings said consumers were likely to believe the size related to the weight of the bird without stuffing and marinade. For a size 20 chicken, the difference between the labelled weight and the actual weight was 300g to 400g.
The Poultry Industry Association of New Zealand has changed its labelling standards for fresh whole chickens as a result of the investigation. Ingham and Tegel will amend their packaging to meet the new standards and the size labelled will be the net weight of the chicken.