The Gisborne based powerlines company Eastland Network has been ordered to repay customers more than $300,000 by the Commerce Commission.
The Commission ordered the refund because Eastland earned more revenue than it was allowed to last year.
Because the company holds a monopoly in the area, there's a limit on the revenue it can earn under the law.
This affects how much consumers pay for lines charges in their electricity bills.
The commission found the breach wasn't intentional, and Eastland made mistakes in some of its pricing.
Eastland serves around 26,000 customers in Gisborne, Wairoa and the North Island's East Coast.