Police have been called in to investigate letters sent to Department of Conservation workers from anti-1080 protesters threatening to wage war against the group.

An aggressive letter threatening DOC staff and claiming more sika deer would be released - which would put local stock at risk of TB disease - was sent to the group in a bid to halt its use of 1080.

The letter follow closely behind a threat to bring down DOC helicopters if it drops the pesticide in Taranaki's Egmont National Park.

"This will be a war like no other, you watch this happen around you," it reads.

Advertisement

"We will take down helicopters who support 1080 drops."

The letter also claimed protesters would poison milk and target the inside of meat processing companies if use of the pesticide continued.

The note was the second of its kind. In October an anonymous letter which claimed a group of sika deer released in Taranaki forests in October was in retaliation for 1080 operations was sent to DOC.

In this incident, workers were forced to frantically track down the herd of deer running through the conservation forests after receiving an anonymous tip off.

Director General of Conservation Lou Sanson confirmed DOC had called in police to investigate following the latest incident. DOC would not be speculating upon who wrote the letter or why, he said.

"These threats to DOC staff are taken very seriously and will not be tolerated. I am appalled that someone would threaten our staff in this way as they are trying to go about their daily work to protect our native species and wildlife."

Sanson said DOC staff had been victim to a handful of other threatening actions in recent months.

The department laid a complaint with police after the cars of its staff working on pest control had their wheel nuts loosened, apparently by anti-1080 protesters.

In the worst case, the wheel of the DOC contractor's car came off while he was driving and jammed in the housing around the wheel.

At the time, director-general Lou Sanson said it was fortunate no one was hurt.

He believed the alleged tampering was designed to intimidate staff working on pest control operations involving the controversial poison 1080.

A complaint has also been laid with police in relation to 1080 baits being placed in a DOC worker's letterbox.

Sanson said it was important his staff were able to get on with their job of protecting conservation areas without fear of being harmed or harassed.

"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."