Vector is to be stung with a yet-be-determined financial penalty due to the length of Auckland power outages in 2015 and 2016.
The lines company is being prosecuted by the Commerce Commission for what the regulator said was an "excessive level of power outages".
The commission is filing High Court action against Vector under the Commerce Act alleging the company failed to adhere to good industry practice in some aspects of its network management, which resulted in increased outages over 2015 and 2016.
Vector isn't contesting the charges and the commission says it has also reported further breaches of its quality standards for 2017 and 2018 that are subject to a separate investigation.
More details are likely to emerge during a High Court penalty hearing. It is understood a date for this has not been set and the NZX-listed firm could face a fine of up to $5 million.