Auditor-General Lyn Provost has been asked to investigate the Government's deal with SkyCity.
The Auckland casino was selected last year as the preferred bidder to build an international convention centre and is negotiating a deal with the Government for more pokies in exchange for footing the $350 million bill for the centre.
Prime Minister John Key has said SkyCity was one of several companies approached about the contract in 2009, and the Green Party has questioned the apparent closeness between the Government and the company.
Co-leader Metiria Turei today requested that Ms Provost launch an investigation into the process that led to SkyCity being the preferred bidder, and look at Mr Key's and Economic Development Minister Steven Joyce's involvement in the deal.
Mr Key has said that he approached SkyCity personally in his capacity as Tourism Minister.
"John Key's pokies-for-convention-centre deal raises a host of very serious issues about ministerial influence and the fairness of the process to other groups who put together proposals to build a centre," Mrs Turei said.
"We believe that several state sector guidelines and rules for the procurement of public services have potentially been breached."
Mrs Turei said if an inquiry showed that SkyCity had received an unfair advantage, then the process needed to start again.
"We have also asked the Auditor-General to investigate whether the long-term known economic costs from gambling harm have been factored into the cost of the deal."