Online electricity retailer Powershop says a ruling against unprecedented charges to major power users is a victory.
It says a draft ruling by the Electricity Authority shows big spikes in prices will not be tolerated.
Genesis Energy charged up to $20,000 a megawatt hour on 26 March during a scheduled maintenance shutdown in the Upper North Island - a price hundreds of times higher than the average for that month.
The Electricity Authority wants to drastically cut the amount, in a draft decision that is now open to further submissions.
It received 35 complaints from banks, hospitals, Telecom, Vodafone and TVNZ.
Powershop was another, arguing that the cost to it would be $1.7 million higher than on an average Saturday. Without the authority's decision, it said, such spikes on the wholesale market could have become almost routine.
Genesis says the price it charged reflects the cost of firing up the Huntly power station, and there were chances to buy cheaper power beforehand.
In its draft ruling the Electricity Authority said Genesis Energy did not break any laws but a so-called undesirable trading situation prevailed.