(a) Proposed budgets; adjustments; determination.--The commission may, by regulation, require any class of public utilities, except common carriers, to file proposed budgets with the commission on or before the first day of each budgetary period, showing the amount of money which each public utility within such class, will in its judgment, expend during the budgetary period for payment of salaries of executive officers, donations, advertising, lobbying expenses, entertainment, political contributions, expenditures, and major contracts for the sale or purchase of facilities, and all items covering or contemplating any payment to any affiliated interest for advice, auditing, associating, sponsoring, engineering, managing, operating, financing, legal, or other services. Adjustments or additions to any such budget may be made from time to time by filing supplementary budgets with the commission. When any such budget or supplemental budget has been filed, the commission may examine into and investigate the same to determine whether any or all of the contemplated expenditures are unreasonable or contrary to the public interest and if after reasonable notice and hearing, it shall so determine, it shall make its findings and order in writing rejecting the same or any part thereof.

(b) Rejected budgets.--Upon such rejection, the public utility concerned shall not make further expenditures or payments under the budget or part thereof rejected, and no expenditures at any time made under such rejected budget, or part thereof, shall be allowed as an operating expense, or capital expenditure in any rate or valuation proceeding, or in any other proceeding or hearing before the commission, unless and until the propriety thereof shall have been established to the satisfaction of the commission, and any such finding or order shall remain in full force and effect, unless and until such finding or order shall be vacated, modified or set aside by the commission, or upon an appeal, as provided in this part.

(c) Use of budgets.--The filing of any budget, its examination, investigation, or determination by the commission, under this section, shall not bar or estop the commission from determining, in any rate valuation or other proceeding, whether any or all of the expenditures made under any budget or supplemental budget are reasonable or commensurate with the service or facilities received.