Climate campaigner Cindy Baxter fears carbon trading has been put at risk by New Zealand's position on greenhouse gases.
A United Nations meeting in Doha on Saturday decided to extend the life of the Kyoto Protocol until 2020, but New Zealand was one of four countries that voted against.
Ms Baxter said New Zealand will now be shut out of trading with the European carbon market as a result of its position.
She said that could leave companies that have already bought carbon credits dangerously exposed.
Climate Change Minister Tim Groser said the Emissions Trading Scheme is secure until a new deal is signed, most likely in, 2015.
New Zealand announced on 9 November that it would not sign up to phase two of the Kyoto Protocol.