The Commerce Commission is appealing a High Court ruling over the setting of prices for energy networks.
The High Court had ruled in favour of Vector's Judicial Review appeal against the commission, saying the regulator had failed to provide a full picture of how it calculated the prices that network firms could charge customers.
But the commission says it does not think the input methodology for starting prices was intended when Part 4 of the Commerce Act was enacted.
Chairman Mark Berry says he's also concerned the High Court's decision could potentially require the commission to develop other process input methodologies that it does not believe were intended by Parliament.
Dr Berry says the decision leads to uncertainty and the potential for further legal challenges, and it is in everyone's interests to address the concern now.
Vector says it will take part in the appeal process, but it is disappointed the commission has taken the appeal, which will lead to a continuation of an extremely costly and lengthy process, and further delay regulatory certainty.
Shares in Vector fell 2 cents to $2.52 on Friday.