Washington state Attorney General Bob Ferguson is urging the Utilities and Transportation Commission to require Avista to refund customers up to $41 million for rates that violated state law. 

According to the Washington State Attorneys General's Office, a written testimony filed on Friday says Avista should be required to refund customers for overcharges from January 11, 2016 through April 30, 2018. 

During that period, Washington residents and businesses were charged $41 million more than they should have under state law. 

Residential customers were over charged roughly $40 per customer. 

Avista serves about 253,800 electric customers and 167,000 natural gas customers in Eastern Washington. 

The Utilities and Transportation Commission will issue a final decision on the refunds after a hearing on October 30.