Support for a supermarket code of conduct is growing and the Green Party says there must be an independent watchdog to oversee it.
MP Sue Kedgley sparked a controversy over vegetable and fruit prices on Sunday when she said a survey found supermarkets were marking up produce by up to 500 percent while growers struggled to survive on the prices they were being paid by the two big chains.
She called for an investigation and suggested a code of conduct for supermarkets.
Since then the Food and Grocery Council, and the supermarkets, have denied markups anywhere near 500 percent but they have given guarded support to establishing a code similar to one operating in Britain.
Ms Kedgley said today the supermarkets seemed to want a voluntary code.
"The Green Party will not support anything that is merely a public relations exercise to assist them dodging the tough questions on their pricing policies," she said.
"For the sake of New Zealand's fruit and vegetable growers it is essential that any supermarket code of conduct is negotiated with growers and Horticulture NZ, and is backed up by an independent arbitrator."
Ms Kedgley said Britain initially had a weak voluntary code which proved ineffective.
"A strengthened supermarket code has since been set up and the position of an independent supermarket ombudsman has got the go ahead," she said.
Food and Grocery Council chief executive Katherine Rich, whose organisation is in the middle between the growers and the supermarkets, says consumers aren't being ripped off and 500 percent markups don't happen.
"There are lots of costs that are incurred throughout the supply chain," she said yesterday.
"A lot of goods get thrown away."
Growers want an investigation and say they aren't being paid more for vegetables and fruit than they were five years.
"As a general rule retail prices are between 100 percent and 200 percent higher than the wholesale price, but sometimes it can be much higher than that," said Horticulture NZ chief executive Peter Silcock.