The Government is refusing to disclose official advice about a proposal to increase the number of gaming machines at Sky City casino in Auckland as part of a deal to build a new convention centre.
In response to a request under the Official Information Act, outgoing Internal Affairs Minister Amy Adams refused to release reports she has received about the proposal.
Mrs Adams did release a small part of a weekly report she received but comments were deleted on the basis they could prejudice commercial negotiations.
Three other reports were withheld for the same reason.
Labour says it is reprehensible that such information is being kept secret.
Green Party co-leader Russel Norman says the Government is consistently using commercial confidentiality as an excuse for not releasing information and that is not good enough.
Radio New Zealand's political editor says Prime Minister John Key has put the cost of the convention centre at more than $300 million.