The Green Party wants the Auditor-General to look into how SkyCity was chosen as the preferred bidder to build a national convention centre in Auckland.
Co-leader Metiria Turei has written to Lyn Provost claiming a potential breach of state sector guidelines and rules for the procurement of public services over the process.
She has asked for an investigation into the roles played by Prime Minister John Key and Economic Development Minister Steven Joyce and well as the expressions of interest process.
"It is important that all the normal rules around government procurement have been followed.
"If the rules have not been followed, and SkyCity has received an unfair advantage, then the process needs to start again," she said.
A deal for SkyCity to build the $350 million centre in Auckland is being negotiated and Mr Key says it has almost been sealed.
It has been criticised because of SkyCity's wish to increase the number of pokie machines in exchange for building the centre.
The Greens and other opposition parties are against it and claim the government is "selling legislation".
"The Green Party believes it is wrong to change the law so SkyCity can get hundreds more pokie machines when all credible research shows that increased opportunities to gamble equals increased social harm," Mrs Turei said.
Mr Key says the centre will employ 800 once it opens will need 900 to build it and will result in 200,000 more visitor nights a year once it is operational.
He has strongly rejected claims from the opposition that he interfered in the tender process.