Department of Conservation staff working on pest control have had the wheel nuts on their cars loosened, apparently by anti-1080 protestors.
The department has laid a complaint with the police after three cars being driven by a DOC staff member, a contractor and a member of the public were allegedly tampered with.
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.
DOC director-general Lou Sanson said it was fortunate that no one was hurt. His department believed the alleged tampering was designed to intimidate staff working on aerial pest control operations involving the poison 1080 - though not all of the cars affected were working on pest control projects.
"People have a right to lawful protest, but I will not tolerate anyone putting my staff at risk as they go about their job of protecting our precious wildlife," he said.