The Department of Conservation has received a letter claiming responsibility for the "eco-terrorism" release of deer into Taranaki forest.
The letter sent to DOC also threatened to "take down helicopters" that support 1080 drops.
The three-page handwritten letter was sent by a group calling itself New Zealand Hunters, who claim to have more guns than the police and said they would bring DOC to its knees.
The letter also said it was responsible for releasing sika deer into Taranaki forests in October in retaliation for 1080 pest control.
It said it had released 25 more into area between Waverly and Tarata.
And it said the poison was banned in Europe and the United States but was spread widely in New Zealand.
The letter also threatened to contaminate milk and meat with 1080.
DOC has condemned the letter and asked police to investigate.
"These threats to DOC staff are taken very seriously and will not be tolerated," the department's director general of conservation Lou Sanson said.
"Apart from a few isolated cases, the feedback we get is that most New Zealanders strongly support DOC's work to protect our native species and habitats and understand why we need to use 1080 as part of our war against predators," he said.
DOC said it has culled 17 of the estimated 30 deer released in October.
Activist says letter sent to 'undermine' anti-1080 groups
An anti-1080 activist believes a letter declaring war on the Department of Conservation has been written to undermine environmentalist groups.
The chair of 100 Percent Pure Taranaki, Chris Wilkes, said he did not think anyone from his group would be so antagonistic.
"It's really not in anyone's nature to be so aggressive and so outrageous and basically radical and it really strikes me as strange."
Mr Wilkes said he believed the letter writer had ulterior motives.
"It just strikes me that someone is trying to pose as an anti-1080 protester to undermine everyone.
"And that's what a letter like this does, it really undermines the credibility of respectable New Zealand citizens who have legitimate concerns about the indiscriminate use of 1080."
Mr Wilkes said his group was more interested in promoting alternative methods of pest control to 1080 than attacking DOC.
He said he would be talking to the police about people who have threatened his group in the past.
North Taranaki Deerstalkers Association president Tom Ryder said he was at a loss to understand who could be behind a letter declaring war on DOC over its use of 1080.
Mr Ryder said hunters were upset about the wholesale use of 1080 but he was not aware of people threatening the Department of Conservation.
"I've not heard any rumours or whispers as to who might be involved but we certainly don't have any affiliations with those sorts of people."
He questioned whether the number of deer mentioned could even be sourced easily and said the letter writer was obviously from outside the mainstream hunting community.