New Zealand authorities said Tuesday they had received a "criminal threat" to poison baby formula and were taking it seriously, warning parents to examine packaging for signs of tampering.
Police said small packages of baby formula containing poison had been sent with anonymous letters to the National Farmers Federation and dairy giant Fonterra.
"Whilst there is a possibility that this threat is a hoax, we must treat the threat seriously and a priority investigation is underway," deputy commissioner Mike Clement said.
Clement said the letter-writer threatened to contaminate baby formula with a poison called 1080, which is commonly used for pest control in New Zealand.
He said the threat, originally made in November, was to contaminate products unless 1080 was banned by the end of March.
The poison is used to control feral pests such as cats and possums, but some critics argue it damages the environment and kills native wildlife.
Baby formula is a multi-billion dollar export industry for New Zealand and the Ministry of Primary Industries said it was confident the product remained safe.
"The ability for anybody to deliberately contaminate infant and other formula during manufacturing is extremely low," deputy director-general Scott Gallacher said.
"Regardless, we encourage people to be vigilant when buying infant and other formula. Our advice is always to check packaging for signs of tampering. We are reinforcing that advice as a result of this blackmail threat."
Clement said a team of 36 officers had been investigating the threat since November and appealed for public assistance tracking down the blackmailer.
The New Zealand Food and Grocery Council said extra testing had been introduced to reassure parents, although it said it had "absolute confidence" that products on shelves were safe.
"This is an attack on Brand New Zealand," it said.
"Our country has a reputation for producing safe, high-quality food products which are in demand around the world, and this coward's letter doesn't change that at all.
"These letters are an attack on all New Zealanders, designed to gain publicity and cause the maximum damage to the New Zealand economy."
The threat comes as the country's dairy industry is recovering from a botulism scare last year that saw potentially toxic formula yanked off shelves from China to Saudi Arabia before it was declared a false alarm.