1080 opponents have condemned those behind the baby formula threat letters, branding them "irresponsible" and their actions "total stupidity".
Wairarapa conservationist and author Bill Benfield, who has penned a book about 1080 in New Zealand, was perturbed by the threats when the news broke yesterday.
"It is absolutely stupid," he said. "It's not even a protest, it's stupidity."
Mr Benfield did not know of any 1080 opponents who would do something so extreme for the cause.
"There's no anti-1080 movement out there as such, there is no one group. It's just lots of individuals putting in their effort and working together.
"I pretty much know everyone, and I don't know anyone that's as stupid as that.
"The Government's use of 1080 is stupid - and that's about the most polite thing I can say about it.
"For anyone to make a threat like this is equally as stupid. I don't know who did it but I don't think it's anyone in my circle."
Tony Orman, a Blenheim-based opponent of 1080, described the method of protest as "totally irresponsible".
"I can understand people being absolutely frustrated with the Government's pig-headedness around 1080 and the continued use of it ... and I'm not surprised at their frustration. But I don't condone their form of protest."
Mr Orman said 1080 use caused irreparable harm to the environment and needed to be challenged but this protest was unacceptable.
"I definitely don't condone it and it just doesn't do any good at all for anyone to try these sort of tactics."
Anti-1080 campaigner Carol Sawyer said threatening babies was the "lowest of the low".
However, she believed the situation did raise a series of questions.
"Why on earth have they taken from November to release the letter? ... And who has access to pure 1080? It's a highly deadly poison in its pure form, it should be kept under lock and key.
"It's extremely worrying if someone's flinging pure 1080 around. It's not something that should be available to anybody really."
Few pesticides arouse such intense feelings between users of 1080 and opponents of the toxic substance, partly because pest baiting campaigns in the past have killed non-target species such as dogs, cattle and deer.
A majority of scientists support the use of 1080 in pest control, and their work has been important in devising more effective ways to spread the pesticide baits and to reduce the amount of actual poison in pellets laced with the substance.
What is it?
Sodium fluoroacetate is a poison mixed into baits and used to control a range of pests, especially possums, rats and stoats.
Why is it used in New Zealand?
The main threat to many native plants and animals comes from introduced predators. 1080 is effective in controlling these pests and well suited to conditions here. It can be applied by air and is the most cost-effective method of large-scale pest control over difficult terrain.
Why do people oppose it?
Opponents believe 1080 is inhumane and causes animals and birds to suffer for hours or days before dying.