5 U.S.C. § 8346 : US Code - Section 8346: Exemption from legal process; recovery of payments

      (a) The money mentioned by this subchapter is not assignable,
    either in law or equity, except under the provisions of subsections
    (h) and (j) of section 8345 of this title, or subject to execution,
    levy, attachment, garnishment, or other legal process, except as
    otherwise may be provided by Federal laws.
      (b) Recovery of payments under this subchapter may not be made
    from an individual when, in the judgment of the Office of Personnel
    Management, the individual is without fault and recovery would be
    against equity and good conscience. Withholding or recovery of
    money mentioned by this subchapter on account of a certification or
    payment made by a former employee of the United States in the
    discharge of his official duties may be made only if the head of
    the agency on behalf of which the certification or payment was made
    certifies to the Office that the certification or payment involved
    fraud on the part of the former employee.