The Green Party is calling for a Parliamentary inquiry into current genetic engineering trials at AgResearch's Ruakura facility.
Animal welfare spokesperson Sue Kedgley MP says the death of three genetically modified cows, which had been formed using a human genetic code, raises ethical and animal welfare issues.
The six-month old calves died last year, after the code caused their ovaries to grow abnormally large and rupture.
AgResearch says the deaths were reported to the animal ethics committee at the time, and it was cleared of any wrongdoing.
It says the human genes were intended to affect only the cows' mammary glands.