The Government says it's been forced to suspend the sale of Mighty River Power shares to update the offer document following the Opposition's announcement of its policy on electricity.
Last week, Labour and the Greens said if they were in government, they would set up a single purchaser of electricity to help bring down prices.
The Mighty River Power share offer document already lists the potential for regulatory changes as a risk for investors.
However, Prime Minister John Key said on Monday that potential investors should be made aware of the possible impact of the Labour/Greens policy.
Mr Key said that includes how likely it is that Labour and the Greens will be able to form a government after the 2014 election; and if they can, will it be practical or even possible to implement the policy and over what timeframe.
Finance Minister Bill English told Radio New Zealand's Checkpoint programme it is not possible to determine what the impact of the Opposition's policy might be on the shares.
"What we've got to bear in mind here is the share uncertainty of what's been proposed. So if these parties won an election, and they were able to form a government, and they thought they could put that policy in place, then it's possible it could have some some adverse effect."
The Government said the share offer website would be suspended until after midnight on Monday. No applications for shares would be accepted until the site is operating again.
People who have already bought Mighty River Power shares can get their money back if they have changed their mind because of the Labour/Greens announcement.
They have five working days, or until 1 May, to make an application to withdraw their offer.