Greenpeace claims the dairy giant's claim Anchor butter is '100 percent New Zealand grass-fed' - is misleading customers.
It says up to 20 percent of a Fonterra dairy cow's diet could be imported palm kernel.
New Zealand's dairy industry imported more than two million tonnes last year.
Greenpeace claims it's making the grass-fed claim to downplay Fonterra's reliance on palm kernel, which is linked to rainforest deforestation.
Fonterra has confirmed it's received proceedings from Greenpeace - and won't comment further.
