By yesterday afternoon, $641 million had been lost from the combined values of the two electricity generators as investors tried to understand what the two Opposition parties were proposing.
At one stage, there were no buyers in the market for TrustPower - only sellers.
Milford Asset Management senior analyst William Curtayne said if Labour and the Greens formed the next government, and introduced the single buyer model for electricity energy, Contact would have a 20% downgrade imposed.
''We would not price in a full discount because we still wonder would they really do it? There is so little detail and it could be worse than we think.''
KiwiSaver and superannuation schemes would have lost value in the past two days as the share prices fell, he said. Both of the listed companies would be part of most schemes.
The value for Mighty River Power shares, on offer now, would also be affected by the uncertainty in the market.
Mr Curtayne said there was growing concern in financial circles about how hydro assets would be valued under the plan proposed. If long-standing hydro assets of some companies were valued at zero, against existing debt, then they could be holding more debt than assets and be theoretically bankrupt.
''At what point do you grandfather in the values of hydro assets built under the old Electricity Corporation?''
Hydro generators used rainwater, collected in lakes, to run through their plants and create electricity, he said.
Economic Development Minister Steven Joyce said the more than two million New Zealanders in KiwiSaver would have watched with concern as the value of their retirement nest eggs fell sharply within hours of the announcement on electricity pricing by the Greens and Labour.
''If Labour and the Greens could do that in just a few hours, imagine what they would do if ever they got near being in government,'' he said.
Contact chief executive Dennis Barnes told BusinessDesk it was hard to see how the company, which operates the Clyde Dam hydro scheme, would have justified investing $2.5 billion on new power plants if the Labour-Green electricity policy had been in place.
''Competitive and efficient electricity markets attract investment and talent from companies like Contact. Over the past five years, Contact alone has invested over $2.5 billion in building generation capacity to ensure the reliable, safe and secure supply of power to New Zealanders ... ''
The political stoush continued yesterday over the plans by Labour to introduce NZ Power, a single electricity buyer to purchase all electricity generation at a ''fair price'' based on the actual cost of production.
The Green Party proposed every household would get a block of low-cost electricity each month from the savings that NZ Power achieved.
Green co-leader Russel Norman said the Greens' plan would open the door to new competition and innovation in electricity generation and retailing, leading to lower prices.
''National wants to keep the door shut and lock in high power prices to protect the five companies that dominate the electricity sector today.''
When NZ Power tendered for new generation, it would accept bids from whichever companies could offer the best price to build the new power plants while meeting sustainability and reliance requirements.
Energy and Resources Minister Simon Power released a statement quoting former Labour energy minister David Parker saying in 2006: ''a single buyer would likely result in higher capital and operating costs. The risks involved in changing arrangements could be significant. The resulting uncertainty could lead to investment proposals being put on hold.''
In response, Mr Parker said that after a 2006 briefing to the Cabinet, summarising MED's advice on alternatives including amalgamated state-owned enterprises and a single buyer, the overriding concern of Cabinet was the need to avoid investment uncertainty during the transitional period given that electricity margins were at that time perilously thin.
''I have always been on record about my serious concerns about the limits to competition under the Bradford reforms, which costs consumers through higher power bills,'' he said.
