In any proceeding, upon the commission's own motion, or upon application or complaint, involving rates or practices of any public utility, the commission may disallow, in whole or in part, any payment or compensation to an affiliated interest for any services rendered or property or service furnished, or any property, right, or thing received by such public utility, or donation given or received, under existing contracts or arrangements with such affiliated interest unless such public utility shall establish the reasonableness thereof. In such proceeding no payment shall be approved or allowed by the commission, in whole or in part, unless satisfactory proof is submitted to the commission of the cost to the affiliated interest of rendering the service or furnishing the service, property, security, right or thing to the public utility. No proof shall be satisfactory, within the meaning of the foregoing sentence, unless it includes the original (or verified copies) of the relevant cost records and other relevant accounts of the affiliated interest, or such abstract thereof or summary taken therefrom as the commission may deem adequate, properly identified and duly authenticated. The commission may, where reasonable, approve or disapprove such contracts or arrangements without the submission of such cost records or accounts.