A.R.S. § 40-365

Under rules and regulations the commission prescribes, every public service corporation shall file with the commission, and shall print and keep open to public inspection, schedules showing all rates, tolls, rentals, charges and classifications to be collected or enforced, together with all rules, regulations, contracts, privileges and facilities which in any manner affect or relate to rates, tolls, rentals, classifications or service. The commission may, from time to time, approve or fix rates, tolls, rentals or charges in excess of or less than those shown by the schedules. The commission may, from time to time, determine and prescribe by order such changes in the form of the schedules as it finds expedient, and modify the requirements of any of its orders, rules, or regulations.