26 U.S.C. § 6071: Time for filing returns and other documents

When not otherwise provided for by this title, the Secretary shall by regulations prescribe the time for filing any return, statement, or other document required by this title or by regulations. Returns made under subpart B of part III of this subchapter (other than returns and statements required to be filed with respect to nonemployee compensation) which are filed electronically shall be filed on or before March 31 of the year following the calendar year to which such returns relate. Forms W–2 and W–3 and any returns or statements required by the Secretary to report nonemployee compensation shall be filed on or before January 31 of the year following the calendar year to which such returns relate. For payment of special taxes before engaging in certain trades and businesses, see section 4901 and section 5732. Except as provided in paragraph (2), the amendments made by this section [amending this section and section 6402 of this title ] shall apply to returns and statements relating to calendar years beginning after the date of the enactment of this Act [ Dec. 18, 2015 ]. The amendment made by subsection (b) [amending section 6402 of this title ] shall apply to credits or refunds made after December 31, 2016 .”