(1) Except as provided in subsection (2) of this section, no change shall be made by any utility in any rate except upon thirty (30) days' notice to the commission, stating plainly the changes proposed to be made and the time when the changed rates will go into effect. However, the commission may, in its discretion, based upon a showing of good cause in any case, shorten the notice period from thirty (30) days to a period of not less than twenty (20) days. The commission may order a rate change only after giving an identical notice to the utility. The commission may order the utility to give notice of its proposed rate increase to that utility's customers in the manner set forth in its regulations.
(2) The commission, upon application of any utility, may prescribe a less time within which a reduction of rates may be made.