The lines company Vector has lost a Supreme Court challenge to the way in which price controls are set by the Commerce Commission.
Thursday's Supreme Court judgement upholds an earlier Court of Appeal judgement, which ruled in the commission's favour.
In setting price controls for the current five-year regulatory period, the Commerce Commission rolled over the prices applicable at the end of March 2010.
Vector disputed that and claimed the commission was obliged to publish the methodology it had used to set the prices, which it had not done.
The Supreme Court has unanimously rejected Vector's appeal and concluded that the legislation did not require the commission to publish information about the method it used to reset the starting prices.