The Electricity Authority has reversed high electricity prices charged by Genesis Energy in March, saying they threatened the stability and integrity of the wholesale market.
Wholesale prices soared to nearly $20,000 a megawatt hour, following a planned maintenance shutdown on the national transmission grid in the upper North Island.
It prompted a flurry of complaints that the prices were four times higher than previous power interruptions in the past and accusations that state-owned Genesis Energy was price-gouging.
The authority says Genesis did nothing wrong, but says if companies did pay those prices confidence in the market would be undermined.
It is proposing that the prices during the shutdown period should be slashed to between $1500 and $3000 per megawatt hour.
Labour's energy spokesperson David Parker says Genesis has been exposed for an outrageous act of corporate greed.
"To try and and take $57 million instead of their normal charges - which would have been a mere fraction of that - was always going to be so excessive that it was going to be turned over."
Mr Parker told Checkpoint the case is just the tip of the iceberg and other power generators are also acting anti-competitively.
