Meridian Energy says customer demand for electricity dropped off over the weekend as a result of a previous price hike.
Wholesale prices soared to $20,000 a megawatt hour in the last weekend of March, following a six-hour planned maintenance shutdown on the national transmission grid in the upper North Island.
During a similar shutdown took place on Saturday prices remained well below a $100 per megawatt hour - which is what Meridian Energy markets and production general manager Neal Barclay says it would have expected the previous weekend.
The Electricity Authority is investigating the earlier price spike. Mr Barclay estimates Meridian's losses to be about $15 million to $16 million.
Mr Barclay said its 60 customers which are exposed to spot prices reduced their consumption at the weekend, because of the previous price rise.
He says that's concerning because it presumably means the firms reduced production, which could flow through to GDP.
Fourteen parties, including ASB and the New Zealand Refining Company, have lodged complaints about the price spike, and one business group wants the Government to take action.