The Environment and Conservation Organisation fears an expanded Environmental Protection Authority will not have enough resources or powers.
The Government has announced the agency will be an independent, one-stop shop for resource consents not covered by regional councils.
However, ECO says the Department of Conservation has been starved into submission with funding cuts, and the same could happen with the EPA.
But the agency is being welcomed by many others, including Federated Farmers.
The Sustainability Council says the EPA is necessary because the Ministry for the Environment has spent two decades giving advice instead of delivering outcomes.
Executive director Simon Terry says it's vital that core protections in the Hazardous Substances and New Organisms Act are not lost.