Mighty River Power has warned would-be investors of a long-term drop in electricity prices which would hit the value of its shares should the Tiwai Point aluminium smelter close.
The company yesterday released the prospectus for its partial sale, which is scheduled to take place next month.
It reveals the shares will cost $2.35 to $2.80 each, and that retail investors will receive a bonus share for every 25 they buy and hold for two years.
Listing the risks to value of its shares in the prospectus, Mighty River noted its interaction with the wholesale electricity market may adversely affect its financial performance and profitability and, therefore, "the value of its shares and the amount of dividends it may be able to pay shareholders".
It discusses the smelter in a section headed "longer term wholesale electricity market exposure risk" saying a significant reduction in operations at the smelter or even closure "could lead to a sustained reduction in electricity prices in general".
But it did not put figures on the effect on prices and profitability.
"The size of these price reductions, both short term and ongoing, "would depend on many variables," it said.
Despite the Government early this year winning the legal battle over the Mighty River sale against Maori Council claims it was a breach of the Treaty of Waitangi, the company yesterday disclosed other treaty-related risks in its prospectus.
That included the fact the Waitangi Tribunal had the power to order return to Maori of particular "memorialised" parcels of land on which the company has power stations and other infrastructure.
Labour's state-owned enterprises spokesman Clayton Cosgrove said the future of the smelter cast "massive uncertainty" over the Mighty River sale which therefore shouldn't go ahead until the matter was resolved.
Green Party Co-leader Russel Norman said the Government had failed to give investors adequate information about the significance of the Tiwai Point, Treaty claim and other risks.
The prospectus' "bland summary" of risks might be adequate for professional investors, "but it is not good enough when National is trying to lure thousands of Kiwi families into the sharemarket for the first time".
Finance Minister Bill English said the prospectus couldn't include "a guess about the effect of electricity prices because I'm not sure that anyone could know for sure".