The proposals, released by Labour leader David Shearer and Green co-leader Russel Norman, lacked detail but still saw value knocked off listed companies Contact Energy and TrustPower, Mr Curtayne said from Auckland.
Interfering in the market would be a signal New Zealand was not a safe place to invest.
The two parties were against the partial sale of Mighty River Power and other state-owned electricity generating companies.
Mr Curtayne said having the parties suggest setting up NZ Power to purchase all electricity generation would send the wrong message to potential investors in New Zealand companies.
''It's difficult to know how serious they are. Having this come out during the sale process of Mighty River Power is not perfect. It smells of something to try and stop the process.''
Labour leader David Shearer said in a statement the annual average household power bill had risen by nearly $770 over the past 15 years. Prices were rising faster in New Zealand than in many other countries.
Mr Curtayne said prices had risen in the past 15 years but they had risen faster under a Labour-led government than under the current Government.
He was forecasting electricity prices to remain flat, or possibly decline, in the future. If the Tiwai Point aluminium smelter closed, excess generation capacity could mean lower prices.
''It's funny timing. This is not a typical scheme used around the world. It lacks on detail so it may be released now to buy themselves more time,'' Mr Curtayne said.
BusinessNZ chief executive Phil O'Reilly said the proposal would destroy a functioning market and replace it with heavy-handed bureaucracy.
''Inserting an army of bureaucrats between power generators and retailers would destroy price signals, so prices would not reflect the cost of generation.
''In that situation, the taxpayer would continue to pay ever higher subsidies of the electricity system. This is not sustainable.''
The Electricity Authority said on Wednesday that the electricity market was as competitive as it has ever been. It could always be improved, and this was where the focus should be, he said.
A state-controlled sector, as envisaged by Labour, would drive out private investment. The private sector power companies would have to seriously consider their future in the market. Those who had invested heavily would find their profits confiscated, Mr O'Reilly said.
Mr Shearer said that under Labour's plan, the average household's power bill would be cut by between $230 and $330 a year. That was a reduction of more than 10% for residential users. Commercial and industrial users would have their bills reduced on average by 5% to 7%.
''I'm not prepared to sit back while power companies cream super profits at the expense of households and the economy. National's asset sales plan will make the problem even worse when overseas and corporate investors push for higher returns on their investment,'' he said.
Labour would set up a single buyer, NZ Power, to purchase all electricity generation at a ''fair price'', based on the actual cost of production. That would mean more than $500 million dollars would be transferred from the coffers of the power companies directly into the back pockets of New Zealanders.
The Crown would forgo dividends and tax revenue from the power companies, Mr Shearer said. The impact on government accounts would be between $60 million and $90 million.
Mr Curtayne said it would be difficult to understand how hydro-electricity generators would be compensated as the infrastructure was already established and they were running water through the plant.
Economic Development Minister Steven Joyce described the scheme as '' truly wacky and desperate stuff'' made up in the last minute by Mr Shearer and Dr Norman.
''Their crazy idea to have both a single national purchaser of electricity and to exempt Government-owned companies from both company tax and dividends would effectively demolish private investment in the electricity industry overnight.''
It would also raise real questions as to why any individual or company would want to invest in businesses in New Zealand, Mr Joyce said.
NZ power
LABOUR
Will purchase all electricity generation at a fair price based on actual cost of production. Independent economists estimate the new structure will create at least 5000 jobs and increase GDP by up to $450 million. Crown will forgo dividends and tax revenue from power companies, costing between $60 million and $90 million.
GREENS
Every household will get a block of low-cost electricity each month from the savings that NZ Power achieves, saving each family $300 a year. NZ Power will have to give priority to renewables, energy efficiency and resilience of the electricity system.
