The Green Party says excessive dairying is to blame for contaminants found in Fonterra's milk.
The Ravensdown and Ballance Agri-Nutrients fertiliser companies have suspended their use of nitrate-inhibitor products, after improved testing found chemical residues in milk and milk powder.
The products help dairy farmers reduce nitrate emissions and leaching from farmland.
Greens' trade spokesperson Kennedy Graham said they would not be needed if the Government did not insist on farming the land so intensively in order to increase export earnings.
Agriculture spokesperson Steffan Browning said intensive farming damages New Zealand's clean, green brand.