The Green Party says another incident involving melamine highlights problems with New Zealand's food testing regimes.
The German suppliers of an iron supplement used by Fonterra in fortified milk powder products, say it has tested positive for the melamine, an industrial chemical.
However, the Food Safety Authority says there's no public health risk from products with the supplement, due to significant dilution.
Green MP Sue Kedgley says many contamination scares in New Zealand have been picked up by overseas authorities, which she says highlights the inadequacy of testing programmes at the border.
Last year, six children in China died after consuming milk powder contaminated by melamine. Some of the product was from a company part-owned by Fonterra.