The Green Party says it is inappropriate that Solid Energy helped fund a report criticial of the previous government's Emissions Trading Scheme.
The report, by the New Zealand Institute of Economic Research, was published in April last year and claimed the scheme would impose huge costs on the economy over the next few years.
Solid Energy, a state-owned enterprise, contributed about $214,000 to the study.
Green Party co-leader Russel Norman says Solid Energy was secretly trying to undermine policy of the Labour Government.
However, in a statement, Solid Energy says it was asked by NZIER to contribute to the research.
It says it believed a study on the the impact of the Emissions Trading Scheme on the economy would help the company, but insists the report's analysis was only the opinion of NZIER.
Mr Norman says the NZIER should come clean about what other companies also contributed to the $1.3 million study.
The National Government is setting up a select committee this year to take another look at the scheme, which it says was rushed through by its predecessor.