28 U.S.C. § 1367 : US Code - Section 1367: Supplemental jurisdiction

      (a) Except as provided in subsections (b) and (c) or as expressly
    provided otherwise by Federal statute, in any civil action of which
    the district courts have original jurisdiction, the district courts
    shall have supplemental jurisdiction over all other claims that are
    so related to claims in the action within such original
    jurisdiction that they form part of the same case or controversy
    under Article III of the United States Constitution. Such
    supplemental jurisdiction shall include claims that involve the
    joinder or intervention of additional parties.
      (b) In any civil action of which the district courts have
    original jurisdiction founded solely on section 1332 of this title,
    the district courts shall not have supplemental jurisdiction under
    subsection (a) over claims by plaintiffs against persons made
    parties under Rule 14, 19, 20, or 24 of the Federal Rules of Civil
    Procedure, or over claims by persons proposed to be joined as
    plaintiffs under Rule 19 of such rules, or seeking to intervene as
    plaintiffs under Rule 24 of such rules, when exercising
    supplemental jurisdiction over such claims would be inconsistent
    with the jurisdictional requirements of section 1332.
      (c) The district courts may decline to exercise supplemental
    jurisdiction over a claim under subsection (a) if - 
        (1) the claim raises a novel or complex issue of State law,
        (2) the claim substantially predominates over the claim or
      claims over which the district court has original jurisdiction,
        (3) the district court has dismissed all claims over which it
      has original jurisdiction, or
        (4) in exceptional circumstances, there are other compelling
      reasons for declining jurisdiction.

      (d) The period of limitations for any claim asserted under
    subsection (a), and for any other claim in the same action that is
    voluntarily dismissed at the same time as or after the dismissal of
    the claim under subsection (a), shall be tolled while the claim is
    pending and for a period of 30 days after it is dismissed unless
    State law provides for a longer tolling period.
      (e) As used in this section, the term "State" includes the
    District of Columbia, the Commonwealth of Puerto Rico, and any
    territory or possession of the United States.