Economic Development Minister Steven Joyce says the Government can legitimately offer the Sky City casino a change in gambling legislation - to allow it more pokies - in return for a convention centre.
Businesses are backing the venture, saying that Prime Minister John Key was doing his job by identifying a gap in the market, and approaching Sky City bosses suggesting they bid for the centre project.
But opposition parties have accused the Government of selling legislation in return for the centre.
Mr Joyce, who is leading the negotiations on the centre, says governments change laws all the time to ensure progress is made.
He says the Government had to offer an incentive that would not cost the taxpayer any money.
Auckland International Airport is also backing the Prime Minister's involvement in the Sky City convention centre deal, saying he was doing his job by identifying a gap in the market.
Mr Key, who is also the Tourism Minister, has been criticised by opposition parties since acknowledging he approached Sky City bosses suggesting they bid for the centre tender.
The airport's general manager of corporate affairs, Charles Spillane, says Mr Key's actions were appropriate and necessary.
"It certainly makes sense to approach anyone you think might be relevant to the process and make sure that they are involved so you can ensure you get the best outcomes from a tender process".
Mr Spillane says New Zealand's inability to host large international conferences is a significant concern that Mr Key is right to address.
Full economic analysis sought
The Green Party is calling for a new tender process that includes a full economic analysis factoring in the likely costs of social harm from the deal.
And the Labour Party says the Sky City tender was a one-horse race from the start because of the Prime Minister's intervention.
Official papers show Mr Key told officials in 2009 to stop work on the development of an Auckland convention centre and wait for a Sky City proposal.
Mr Key says officials went through a very thorough and detailed process with all of the bidders.
He says that in 2009 the Government wanted to create jobs but had no money. "As the Minister of Tourism," he says, "I thought it would be a great way of boosting the economy, of growing jobs and of making sure we had a convention centre."
Mr Key also points out that at this stage the Government has not actually concluded a deal with Sky City.