29 U.S.C. § 164: Construction of provisions

Nothing herein shall prohibit any individual employed as a supervisor from becoming or remaining a member of a labor organization, but no employer subject to this subchapter shall be compelled to deem individuals defined herein as supervisors as employees for the purpose of any law, either national or local, relating to collective bargaining. Nothing in this subchapter shall be construed as authorizing the execution or application of agreements requiring membership in a labor organization as a condition of employment in any State or Territory in which such execution or application is prohibited by State or Territorial law. The Board, in its discretion, may, by rule of decision or by published rules adopted pursuant to subchapter II of chapter 5 of title 5, decline to assert jurisdiction over any labor dispute involving any class or category of employers, where, in the opinion of the Board, the effect of such labor dispute on commerce is not sufficiently substantial to warrant the exercise of its jurisdiction: Provided , That the Board shall not decline to assert jurisdiction over any labor dispute over which it would assert jurisdiction under the standards prevailing upon August 1, 1959 . Nothing in this subchapter shall be deemed to prevent or bar any agency or the courts of any State or Territory (including the Commonwealth of Puerto Rico, Guam, and the Virgin Islands), from assuming and asserting jurisdiction over labor disputes over which the Board declines, pursuant to paragraph (1) of this subsection, to assert jurisdiction.