Mercury Energy customers face price rises of almost 5%.
It is increasing electricity charges by 3.9% for those living in West Auckland and from the North Shore - Wellsford.
The company is also passing on an increased cost of using the lines.
That will mean northern customers will face price rises of 4.9%, about $6.30 extra a month.
Customers in Auckland's CBD and Papakura areas will face an increase of 2.2% - about $2.70 a month.
Mercury Energy has almost 300,000 residential customers across New Zealand.