AUGUSTA, Maine (AP) _ The outside group hired to investigate complaints about Central Maine Power bills is expanding its review to include the utility’s customer service performance.

The Maine Public Utilities Commission this week authorized Liberty Consulting Group to look at customer service and communications in addition to the billing and metering issues that sparked the probe.

The PUC is also conducting its own investigation of CMP’s metering, billing and customer service performance, in tandem with the Liberty audit.

The billing and metering questions followed complaints from thousands of customers of spikes in their bills last winter. Pennsylvania-based Liberty will be paid about $400,000 for its work. The company was hired after a public bidding process.