A national, legally binding definition of free range may have to be created, the Government says, after a major supermarket supplier was found to be passing off caged eggs as free range.

"In time it may get to that point," Primary Industries Minister Nathan Guy told reporters at Parliament this morning.

"It is very difficult at the moment, as I understand it, to determine what is free range."

An investigation by Newsroom found that two brands, Palace Poultry and Woodland, had sold potentially millions of caged eggs with free range packaging.

The eggs came from the same farm in Ararimu, south of Auckland, which is now being investigated by the Serious Fraud Office.

Primary Industries Minister Nathan Guy told reporters at Parliament this morning:
Primary Industries Minister Nathan Guy told reporters at Parliament this morning: "It is very difficult at the moment, as I understand it, to determine what is free range." Photo / Warren Buckland

Australia last year created a legally binding, national definition for free range. Hens must have "regular and meaningful" access to the outdoors, and the density of chickens outdoors must be no greater than one hen per square metre.

In New Zealand, there is a code of welfare for layer hens which includes minimum standards, but the standards are not prescriptive and there are no penalties for non-compliance.

Asked by media what he thought free range meant, Guy said: "I'm not going to get into that. Me trying to define it in front of the television at the moment wouldn't be appropriate."

Farms are audited by the Ministry for Primary Industries (MPI), but these checks only cover food safety and animal welfare concerns.

Guy said the Ararimu farm was inspected by officials recently and no concerns were found.

"It got a clean tick of health for that. In terms of the labelling, that is not something that MPI gets involved with."

Labour leader Andrew Little said a clear definition of free range in New Zealand "would be very helpful".

He said it was up to consumer affairs agencies to detect any misleading marketing, and he hoped they were resourced well enough to do this job.