26 U.S.C. § 859

(a) General rule For purposes of this subtitle— (1) a real estate investment trust shall not change to any accounting period other than the calendar year, and (2) a corporation, trust, or association may not elect to be a real estate investment trust for any taxable year beginning after October 4, 1976 , unless its accounting period is the calendar year. Paragraph (2) shall not apply to a corporation, trust, or association which was considered to be a real estate investment trust for any taxable year beginning on or before October 4, 1976 . (b) Change of accounting period without approval Notwithstanding section 442, an entity which has not engaged in any active trade or business may change its accounting period to a calendar year without the approval of the Secretary if such change is in connection with an election under section 856(c).