Minn. Stat. § 237.22: DEPRECIATION; AMORTIZATION.

(a) For purposes of a proceeding to determine or investigate any wholesale or retail rate, or to set any universal service support level, the commission may fix proper and adequate rates and methods of depreciation and amortization with respect to a telephone company's property.

(b) All telephone companies shall retain data in sufficient detail for the purpose of determining depreciation accruals and reserves by depreciable telephone plant account. Depreciable plant accounts are those specified by the Federal Communications Commission for the class to which a telephone company belongs. All telephone companies shall maintain, and have available for inspection by the commission upon request, adequate accounts and records related to depreciation practices as defined herein.