New figures show power prices have risen by 19 percent since 2009 despite flat or falling demand during the period.
The figures have been released by the Ministry of Business, Innovation and Employment.
Labour's Energy spokesperson David Shearer said the figures reveal power price rises four times the rate of inflation.
He said if the market were working properly, prices would be falling as they are overseas.
But he said they continue to rise, as power companies reap windfall profits, feeding the demand of shareholders after the part-privatisation of government-owned power companies.