Ind. Code § 8-1-2-54
Upon a complaint made against any public utility by any mercantile, agricultural or manufacturing society or by any body politic or municipal organization or by ten (10) persons, firms, limited liability companies, corporations, or associations, or ten (10) complainants of all or any of the aforementioned classes, or by any public utility, that any of the rates, tolls, charges or schedules or any joint rate or rates in which such petitioner is directly interested are in any respect unreasonable or unjustly discriminatory, or that any regulation, measurement, practice or act whatsoever affecting or relating to the service of any public utility, or any service in connection therewith, is in any respect unreasonable, unsafe, insufficient or unjustly discriminatory, or that any service is inadequate or can not be obtained, the commission shall proceed, with or without notice, to make such investigation as it may deem necessary or convenient. But no order affecting said rates, tolls, charges, schedules, regulations, measurements, practice or act, complained of, shall be entered by the commission without a formal public hearing.
IC 8-1-2-54