Prime Minister John Key is challenging opposition parties to commit to buying back shares in companies involved in the Government's partial asset sales programme.
Shares in Mighty River Power and Meridian have been floated, and the Government has also sold down its stake in Air New Zealand.
Mr Key said Labour and the Greens forced a referendum on the asset sales issue and, if they were serious, they would commit to a buy-back if they won office.
"If these parties are serious, today's the day they should tell New Zealanders they will borrow that money and buy those assets back," he said.
"If they're not, then they're just not credible on this referendum."
Both Labour and the Greens said they would not commit to any decision about a potential buy-back until they were able to look at the financial conditions - if they were able to form a government after next year's general election.