The Supreme Court has overruled a challenge by Vector to the way the Commerce Commission set the prices companies can charge to transport electricity and gas.
The dispute escalated to the Supreme Court earlier this year after the Court of Appeal overturned a decision by the High Court last year.
Vector has been at loggerheads with the commission and was successful in its application to the High Court for a judicial review over the way the watchdog set the prices companies could charge customers.
The commission wants to cut what the Auckland network operator can charge.
Vector argued the commission should have determined the rules and processes used, or input methodologies, before setting the prices companies could charge over a regulatory period, which lasts five years.
The regulatory regime started in April 2010, but the input methodologies weren't published until the end of 2010.
The Supreme Court unanimously dismissed Vector's appeal.
And the Commerce Commission said the process has held it up from implementing regulation which could prevent customers being over-charged.