Police have filed blackmail charges against a man they say threatened to poison infant formula in a case authorities worried could have let to wider fallout for the country's lucrative dairy industry.

Police on Tuesday announced they had arrested a 60-year-old Auckland businessman and charged him with two counts of blackmail following a large investigation.

The arrest came after dairy exporter Fonterra and advocacy group Federated Farmers say they received letters in November threatening to lace infant formula with the poison sodium fluoroacetate, known as 1080, unless conservation authorities stopped using it to kill rodents and other pests.

Police declined to name the man ahead of a scheduled court appearance. Should he be found guilty, the man would face a maximum sentence of 14 years in prison on each charge.