The government has the green light to partially privatise four state-owned energy companies now its asset sales bill has been passed by parliament.

As National MPs applauded the 61-60 vote on Tuesday, opposition parties vowed to continue their campaign against the sale of 49 per cent of the shares in the companies.

"It isn't over yet, the fight will move out of here and onto the streets," Labour leader David Shearer said.

"The government has a wafer thin majority and people are clamouring to sign a petition for a referendum."

Green Party co-leader Russel Norman said voters wouldn't forget the government's actions.

"It is flicking off assets it inherited when it came to office as a short term fix for its financial position."

State-owned Enterprises Minister Tony Ryall said the sale was part of the government's plan to control debt and protect the economy.

"We're not going to be diverted by scaremongering nonsense from opposition parties," he said.

"We had an election on this - Labour had its lowest vote ever and National its highest, we do have a mandate."

The government expects to raise $6 billion from the share float and is going to spend it on schools, hospitals and roads.

It says the alternative would be borrowing money, which it won't do.

Opponents are gathering signatures for a citizens-initiated referendum, and have about 100,000 of the 300,000 they need.

The government says the outcome won't make any difference, and by the time a referendum is held shares in three of the companies are likely to have been sold.

Mighty River Power, Genesis Energy, Meridian Energy and Solid Energy are going to be partially sold with the first share float due in August.

National, ACT and United Future supported the bill. Labour, the Greens, NZ First, Mana and the Maori Party opposed it.