18 U.S.C. § 2101 : US Code - Section 2101: Riots

      (a) Whoever travels in interstate or foreign commerce or uses any
    facility of interstate or foreign commerce, including, but not
    limited to, the mail, telegraph, telephone, radio, or television,
    with intent - 
        (1) to incite a riot; or
        (2) to organize, promote, encourage, participate in, or carry
      on a riot; or
        (3) to commit any act of violence in furtherance of a riot; or
        (4) to aid or abet any person in inciting or participating in
      or carrying on a riot or committing any act of violence in
      furtherance of a riot;

    and who either during the course of any such travel or use or
    thereafter performs or attempts to perform any other overt act for
    any purpose specified in subparagraph (A), (B), (C), or (D) of this
    paragraph -  (!1)

      Shall be fined under this title, or imprisoned not more than five
    years, or both.
      (b) In any prosecution under this section, proof that a defendant
    engaged or attempted to engage in one or more of the overt acts
    described in subparagraph (A), (B), (C), or (D) of paragraph (1) of
    subsection (a) (!2) and (1) has traveled in interstate or foreign
    commerce, or (2) has use of or used any facility of interstate or
    foreign commerce, including but not limited to, mail, telegraph,
    telephone, radio, or television, to communicate with or broadcast
    to any person or group of persons prior to such overt acts, such
    travel or use shall be admissible proof to establish that such
    defendant traveled in or used such facility of interstate or
    foreign commerce.

      (c) A judgment of conviction or acquittal on the merits under the
    laws of any State shall be a bar to any prosecution hereunder for
    the same act or acts.
      (d) Whenever, in the opinion of the Attorney General or of the
    appropriate officer of the Department of Justice charged by law or
    under the instructions of the Attorney General with authority to
    act, any person shall have violated this chapter, the Department
    shall proceed as speedily as possible with a prosecution of such
    person hereunder and with any appeal which may lie from any
    decision adverse to the Government resulting from such prosecution.
      (e) Nothing contained in this section shall be construed to make
    it unlawful for any person to travel in, or use any facility of,
    interstate or foreign commerce for the purpose of pursuing the
    legitimate objectives of organized labor, through orderly and
    lawful means.
      (f) Nothing in this section shall be construed as indicating an
    intent on the part of Congress to prevent any State, any possession
    or Commonwealth of the United States, or the District of Columbia,
    from exercising jurisdiction over any offense over which it would
    have jurisdiction in the absence of this section; nor shall
    anything in this section be construed as depriving State and local
    law enforcement authorities of responsibility for prosecuting acts
    that may be violations of this section and that are violations of
    State and local law.