The insurance industry is wary of a reintroduction of competition to the ACC market, because the costs would be too high.
The Government is seeking support for reforms of accident compensation and the ACT Party is pushing for part of ACC to be open competition.
But the Insurance Council says competition would not solve ACC's problems: underfunding, under-reserved and too many liabilities being carried.
Chief executive Chris Ryan says ACC's under-priced premiums and high liability costs would cost insurance companies too much.
New Zealand's largest general insurer, IAG, also says ACC in its current form is unsustainable.
Chief executive Ian Foy, says coverage would be "very challenging" to price.
Business groups are also wary of increased competition.
The Northern Employers & Manufacturers Association says more insurers would result in increased and unstable premiums.
It also says a full private insurance market would mean more forecasting and budgeting work for employers.