Parliament has passed the legislation that will allow the Government to partially sell four state-owned energy companies.
The Mixed Ownership Model Bill was passed by 61 votes to 60, with the support of two of National's confidence and supply parties, ACT and United Future.
The legislation opens the door for the sale of up to 49% of shares in Genesis Energy, Meridian Energy, Mighty River Power and Solid Energy.
State Owned Enterprises Minister Tony Ryall says the partial sale will give the Government cash upfront in an uncertain economic environment.
Mr Ryall says New Zealand currently owes $52 billion and that is expected to rise to $72 billion in three years.
He says the money from the partial sale of the companies is expected to raise between $5 and $7 billion.
The Labour Party says it will keep fighting the partial sale of state-owned assets, despite the passage of the legislation.
The Greens argue the partial asset sale is a short-term vision which most New Zealanders do not support.
Labour vows to fight on
Labour leader David Shearer says people are clamouring to sign a petition to force a citizens-initiated referendum against the sale.
"I can tell you what, the fight is not finished. It will be out of here and on to the streets. That's where it's going, that's where we will continue to fight this battle to keep our assets. Because we are taking the petition to have a referendum on these assets sales to the people of New Zealand."
Opposition parties, Grey Power and unions are continuing to collect signatures to force an anti-sales referendum.
Asked on Monday if the Government would change its mind if a referendum expressed strong opposition to the sales programme, Mr Key said that far as he was concerned the Government received a mandate at the last election to carry out the policy.
"The Government's spelled out its position, it's had a referendum - and that's called the general election."
Mr Key said National had been talking about the policy since January 2011 and went to the election in November on that basis.
"Labour and the Greens had it very clearly as their number one opposition and we scored a record result."