A 65-year-old man from New Plymouth has been arrested and charged with four counts of blackmail after threatening letters were sent to the Department of Conservation (DoC).
Four letters relating to the use of 1080 were received by DoC between September 25 2017 and November 6 2018.
Police launched an "extensive investigation" and arrested the man in New Plymouth on Tuesday.
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Central District Crime Manager Detective Inspector Ross McKay says the arrest sends a clear message:
"While we understand the strength of feeling by some in our community about the use of 1080, it is never acceptable for this to be expressed in the form of threats to individuals," he says.
"DoC staff should be able to go about their lawful business without the fear of threats and intimidation."
DoC says these letters were "extremely nasty" and this particular case has been "harrowing".
"It is completely unacceptable for anyone to threaten or intimidate DoC staff. This case demonstrates that action will be taken when any criminal offending occurs," says director general Lou Sanson.
"DoC staff need to be able to get on with their job of protecting conservation areas without fear of being harmed or harassed."
On Tuesday Newshub revealed that violence and threats of violence by the fringe protesters have spiked - including multiple threats against the Prime Minister and DoC workers.
In January, five incidents were recorded. That number peaked at 93 incidents last month, but DoC is being more robust in its reporting.
And Ms Ardern told Newshub she's received at least one death threat from anti-1080 extremists.
Det Inspt McKay warns this is unacceptable.
"We take very seriously any threats of this nature," he says.
"Anyone considering resorting to unlawful means to advance their cause in this way should think very carefully about the consequences of their actions, and know that police will thoroughly investigate."
The man will appear in the New Plymouth District Court on Thursday.
Police continue to investigate the illegal release of Sika deer into the Taranaki conservation area.