Electricity generator Trustpower has asked the High Court to quash planned changes to transmission pricing.
Trustpower said a fundamental change to transmission charges must be well justified and did not believe this was the case.
The Electricity Authority published its final decision in relation to the setting of transmission pricing guidelines last month.
The changes might have saved Southland consumers up to $80 a year, but bills may have gone up for central North Island households.
The Authority had since asked Transpower to prepare a new transmission pricing methodology for approval.
However, last week Trustpower appealed to the High Court on the grounds of errors of law, asking that the TPM guidelines and Electricity guidelines decision be quashed.
It asked the court to consider whether the Authority inflated its role while restricting Transpower's expertise in the development of the new pricing method, and whether the Authority had the information that justified creating an entire new pricing method.
The appeal has been filed by Trustpower alone, despite other parties publicly opposing the planned changes.
Trustpower also planned to file an application for judicial review.
The High Court has yet to set a date for the hearing.