Fonterra has pulled some of its milk off shelves in the lower North Island after receiving complaints about it having an unpleasant flavour.
It has issued a voluntary recall of several batches of Anchor blue-top milk, but insists it is safe to consume.
Fonterra is now investigating what has caused the change in taste.
Supermarket chain owner Foodstuffs said the milk may have been affected by feed given to cows.
It said customers who have already purchased the affected milk were welcome to return to their local store for a refund.