PORTLAND, Maine (AP) Some Central Maine Power customers are organizing a class action lawsuit against the utility concerning high power bills experienced last winter.

CMP Ratepayers Unite said in a statement Monday attorneys representing the group had retained a New York-based firm to help prepare the suit. The Portland Press Herald reports over 1,000 customers saw high winter power bills during the same period the utility company had billing system problems.

The Maine Public Utilities Commission launched an investigation into the company on March 20. CMP has denied Public Advocate Barry Hobbins’ request for confidential documents related to the power bills.

CMP contends that releasing confidential documents would be burdensome because the utility would have to redact sensitive information.

CMP Ratepayers Unite didn’t say when they would file the suit.