A broker says iwi are hanging on to their carbon credits, meaning their supply is not circulating in the market.
The units are sold and bought under the emissions trading scheme, which was set up to encourage the planting of trees to absorb carbon dioxide. Carbon units were issued to many tribes as part of their Treaty of Waitangi settlements
Nigel Brunel, head of carbon at the futures company OMF, says the stashing of credits has implications for the wider market as there is less supply available for people to buy.
Mr Brunel says there's a view that the Government might auction carbon credits into the market but that Cabinet would rather the forestry sector provided the units.
Buyers are starting to look at the market and wonder where their supply is going to come from. However, Maori organisations are under no pressure or obligation to shift their credits, he says.
Iwi are unlikely to let go of them, because they're a tax free investment and the market is offering low returns, Mr Brunel says.