The Commerce Commission is taking Vector - the Auckland power lines company - to court for excessive power outages in the region.
Vector is not contesting the charge which relates to its performance during the 2015 and 2016 financial years.
Vector is accused of failing to adhere to good industry practice in a number of areas, which the Commission says led to increased outages.
The company says increased stormy weather was a factor, as well as increasing congestion, which meant contractors are less able to quickly travel to sites where work is required.
In a statement to the NZX, Vector said the Commission was alleging that the company had fallen behind on the expected outage resolution times for each year.
"The commission found that Vector breached this quality standard by 51 minutes in the 2015 regulatory year and 13 minutes in the 2016 regulatory year," the company said.
Vector faces a fine of up to $5 million.
The Commission is also currently prosecuting Aurora - a lines company in Otago - for allegedly under-investing in the maintenance and renewal of its network.