26 U.S.C. § 442: Change of annual accounting period

If a taxpayer changes his annual accounting period, the new accounting period shall become the taxpayer’s taxable year only if the change is approved by the Secretary. For purposes of this subtitle, if a taxpayer to whom section 441(g) applies adopts an annual accounting period (as defined in section 441(c)) other than a calendar year, the taxpayer shall be treated as having changed his annual accounting period.