Ark. Code Ann. § 23-4-103: Rates and rules to be reasonable

All rates made, demanded, or received by any public utility, for any product or commodity furnished, or to be furnished, or any service rendered or to be rendered, and all rules made by any public utility pertaining thereto shall be just and reasonable, and to the extent that the rates or rules may be unjust or unreasonable, are prohibited and declared unlawful.