Genesis Energy and Contact Energy have appealed against a regulatory decision that mandated lower wholesale prices after a spike in late March due to a planned maintenance shutdown.
Prices reached $20,000 per megawatt hour, causing an outcry and prompting the Electricity Authority to reset prices at $3000 per megawatt hour to maintain the integrity of the market.
Radio New Zealand's business editor says the authority's decision to declare an undesirable trading situation was contentious, though it found that Genesis Energy, which was blamed for the high prices, did nothing wrong.
Those caught out by the high prices, which included Meridian Energy and Might River Power, argued it was the right decision, while those against, like Genesis and Contact, say it rewarded bad business practice.
Contact and Genesis lodged a High Court appeal against the authority's decision on Wednesday.
Genesis says the decision has created investment and regulatory uncertainty, and it wants assurance about the nature and scope of the market rules in the future.
It says the decision was wrong in principle and in law, and lowers the bar for declaring an undesirable trading situation.
