§ 42-05-451

(a) The commission may classify the public utilities under its jurisdiction and prescribe a uniform system of accounts for each class and the manner in which the accounts and supporting records shall be kept. (b) A public utility shall maintain its accounts on a calendar year basis unless specifically authorized by the commission to maintain its accounts on a fiscal year basis. Within 90 days after the close of its authorized annual accounting period, or additional time granted upon a showing of good cause, a public utility shall file with the commission a verified annual report of its operations during the period reported, on forms prescribed by the commission.