66 Pa.C.S. § 1701: Mandatory systems of accounts.

The commission may, after reasonable notice and hearing, establish systems of accounts, including cost finding procedures, to be kept by public utilities, or may classify public utilities and establish a system of accounts for each class, and prescribe the manner and form in which such accounts shall be kept. Every public utility shall establish such systems of accounting, and shall keep such accounts in the manner and form required by the commission. The accounting system of any public utility also subject to the jurisdiction of a Federal regulatory body shall correspond, as far as practicable, to the system prescribed by such Federal regulatory body. The commission may require any such public utility to keep and maintain supplemental or additional accounts to those required by any such regulatory body.