A group opposed to genetic modification has laid a complaint with the Commerce Commission about advertisements run by poultry processor, Inghams Enterprises.
The Soil and Health Association questions the advertisement's claim that Inghams chickens contain no GM ingredients.
Spokesperson Steffan Browning says there is a possibility that if the chicken's feed includes imported ingredients, it may contain genetically modified material.
The Inghams website says the chickens contain no GM content and are not genetically modified, and points out that the "use of GM soya in feed does not compromise the absolute GM-free status of the poultry products the company produces."
That statement is backed up by Roy Bickerstaffe, professor of food biochemistry at Lincoln University, who says consuming GM food does not make the animal itself genetically modified.
However, Mr Browning argues that most consumers would not think the chicken they are eating could potentially be given feed that contains GM material, and he wants the advertising campaign stopped.
Inghams was not available for comment on Tuesday.
The association representing animal feed manufacturers says while it is the policy of New Zealand companies to source non-genetically modified soya for feed mixes, this cannot be guaranteed most of the time.
Feed Manufacturers' Association executive director Michael Brooks says soya is an important source of protein for chicken and pig feed, and needs to be included.
He says up to 90% of world's soya production is genetically modified.