New Zealand's leading business lobby groups say the Labour Party and the Greens have "ambushed" businesses with their controversial electricity policy which they claim sets a "disturbing precedent" for further intervention.

Labour and the Greens have defended their controversial electricity policy after New Zealand's business leaders issued an open letter asking them to withdraw it.

Editorial: When the Government confirmed its mixed-ownership model strategy, it was taken for granted that Air New Zealand would be the tail-end Charlie.

Keep Our Assets protesters at the National Party's Mainland Region conference say their mock toll booth was so well-received it may be used again.

The Labour-Greens' proposal has created a major dilemma for potential Mighty River Power investors - should they invest in a company that could be subject to major regulatory change, including a dramatic adjustment to its business model?

If Meridian Energy had already floated, it's a fair bet that its share price would have dropped after the Opposition unveiled its electricity policy a week ago.

Both opposition parties will be hoping enough potential investors turn off the pending float so they can declare it a disaster, writes Fran O'Sullivan.

"What just happened?" asks Brian Rudman. "Bland, colourless Labour leader David Shearer has suddenly been transmogrified into a working-class hero."

The war of words over the Opposition's electricity market reform plan has flared again as political opponents traded fire over the plan's economic impact.

Mighty River Power expects it would take at least five years for the Labour and Green party's new electricity policies to be enacted, and John Key says it won't happen.

Investors who applied for Mighty River Power shares have been given a deadline to withdraw their applications if concerned about the Labour-Greens' power policy plans.

Labour's proposed shake-up of the energy sector could slash up to 20 per cent off the value of Mighty River Power although analysts rate the chances of the Opposition's plan going ahead at less than 50 per cent.

As Rio Tinto and Meridian Energy haggle over the price of power for the Tiwai Pt aluminium smelter, optimism about the metal's future has faded.

John Key's partial privatisation programme was dealt a major blow this week when the Labour Party announced proposals to regulate the industry, writes Brian Gaynor.

Millions of dollars of NZers' savings have been wiped after Labour and the Greens announced plans to reform the wholesale electricity market, the Government says.

The Labour-Green proposal to cut Kiwi householders' power prices through radical market reform has been given the thumbs-up by consumer groups, but energy sector commentators are divided on the plan.

The Government says Labour and the Greens are trying to sink the Mighty River Power share float with a hastily drafted threat to impose Soviet-style intervention on the electricity market.

Labour and Greens want Crown-owned single buyer to set electricity prices for generators.

Labour and the Greens are promising a major intervention in the retail power system in a bid to lower residential power prices if they win next year's election.

The Government says it won't be able to say how many people have applied to buy shares in Mighty River Power until after the offer period has closed.

Potential Mighty River Power shareholders have had plenty to digest and dissect since the prospectus for the part-sale of the state-owned enterprise was released this month.