26 U.S.C. § 859: Adoption of annual accounting period

(a) General ruleFor 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 approvalNotwithstanding 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).