The Green Party is calling for an inquiry into dairy pricing, saying there is no real scrutiny of how retail prices are set for milk products.
The main wholesale milk supplier, Fonterra, announced on Friday it would freeze domestic milk prices for 2011.
Progressive Enterprises, which owns the Countdown, Woolworths and Foodtown supermarkets, subsequently announced that it would freeze all milk prices till the end of the year.
Foodstuffs, which runs New World and Pak'n Save, has announced it will only freeze the prices of brands made with Fonterra milk.
The Green Party's food spokesperson, Sue Kedgley, says consumers need transparency into how prices are set.
She says the Greens support Consumer New Zealand's call for a full Commerce Commission inquiry into dairy pricing.
If the Government did not support that action, Ms Kedgley says, it should agree to a select committee inquiry instead.