The Greens called on National yesterday to cancel the sale.
They said it made no economic sense, but Labour rejected any suggestion its new policy had been designed to sabotage the sale.
The decision to suspend the process yesterday to put an additional caution on the prospectus, and to allow cancellations of orders over the next week is a disruption to the float of 49 per cent of Mighty River Power, the first under the Government's partial asset sale plan.
The listing date is still scheduled for May 10 , Prime Minister John Key said yesterday.
But if the Government had known about the Labour-Greens policy at the outset of the process, it would have been included in the prospectus and so it would be included now as an additional risk in the offer document.
Labour and the Greens last week announced a return to central planning for the electricity industry and a move away from market forces.
They said that if they formed the Government after next year's election they would set up a new agency to buy power from generating companies, depending on the cost generation plus what Labour and the Greens deem to be "a fair return on their capital".
The announcement coincided with two polls that showed that Labour and the Greens could win an election if it were held today, which may have had an effect on the market response.
Mr Key said he was legally obliged to let people know the risks, but he appeared to downplay them by saying people would have to make up their minds on the basis of several factors including the likelihood of Labour and the Greens becoming the Government, whether they could implement the policy, the timeframe of any implementation and the effect of the policy.
He said while he could not comment on price or demand for shares, the Labour-Greens policy would be "a huge step backwards for New Zealand".
"A competitive electricity market which we significantly improved in 2009 is bringing down the rate of price increases and is the only way of delivering competitive prices into the future."
The policy meant people would think twice about investing in a country "where the Government can turn around and change the rules on you overnight".
Labour state-owned enterprises spokesman Clayton Cosgrove said that "after five days of going troppo, National has finally calmed down and allowed those who have applied to buy shares in Mighty River Power the opportunity to reconsider".
Labour had recommended that course of action last Thursday.
Greens energy spokesman Gareth Hughes said the purpose of the planned purchasing agency, NZ Power, was not to frustrate the asset sales "but to drive down power prices and eliminate the excessive profits of the electricity companies".
"It is important that Kiwis have the facts on this plan before they decide whether or not to buy shares in Mighty River."
