The organisation which oversees laboratory accreditation says AgResearch was not accredited to carry out testing for botulism causing bacteria in Fonterra milk products.
Fonterra issued an international recall of some infant formula products on 3 August after testing by the institute suggested it could be contaminated.
Tests later proved those fears were unfounded.
International Accreditation New Zealand said that while AgResearch is not accredited to carry out tests for clostridium botulinum, that does not mean it could not do the test accurately.
It said laboratories are normally accredited only for tests they do regularly.