13 U.S.C. § 221 : US Code - Section 221: Refusal or neglect to answer questions; false answers

      (a) Whoever, being over eighteen years of age, refuses or
    willfully neglects, when requested by the Secretary, or by any
    other authorized officer or employee of the Department of Commerce
    or bureau or agency thereof acting under the instructions of the
    Secretary or authorized officer, to answer, to the best of his
    knowledge, any of the questions on any schedule submitted to him in
    connection with any census or survey provided for by subchapters I,
    II, IV, and V of chapter 5 of this title, applying to himself or to
    the family to which he belongs or is related, or to the farm or
    farms of which he or his family is the occupant, shall be fined not
    more than $100.
      (b) Whoever, when answering questions described in subsection (a)
    of this section, and under the conditions or circumstances
    described in such subsection, willfully gives any answer that is
    false, shall be fined not more than $500.
      (c) Notwithstanding any other provision of this title, no person
    shall be compelled to disclose information relative to his
    religious beliefs or to membership in a religious body.