Regulations for milk powder imported from New Zealand into China — the South Pacific nation’s largest market — tightened as sales dropped following the disclosure that letters had been sent to Fonterra Cooperative Group (FCG.NZE) threatening to poison the company’s formula with the toxic pesticide 1080 unless the government stops using it by the end of March, Bloomberg reported. New Zealand milk powder must now have a government certificate and an importer’s examination report to prove it doesn’t contain the pesticide, China’s General Administration of Quality Supervision, Inspection and Quarantine said in a statement.