Canterbury Regional Council commissioner Tom Lambie says proposed changes to the biosecurity system could jeopardise a long-standing weed control programme.
Nassella tussock infests more than 1200 hill country properties in North Canterbury.
It is a highly invasive perennial grass that is unpalatable to stock and difficult to control.
Mr Lambie told Parliament's Primary Production Select Committee that the Biosecurity Law Reform Bill could undermine the council's management of the weed.
He says landowners have until October each year to grub nassella tussock plants, and if they do not comply then the council takes enforcement action against them.
Introducing a challenge to a compliance order in a district or higher court will place on hold ability to manage pests, he said, as rulings are unlikely to occur quickly enough to prevent the seeding of the tussock.