29 U.S.C. § 157 : US Code - Section 157: Right of employees as to organization, collective bargaining, etc.

      Employees shall have the right to self-organization, to form,
    join, or assist labor organizations, to bargain collectively
    through representatives of their own choosing, and to engage in
    other concerted activities for the purpose of collective bargaining
    or other mutual aid or protection, and shall also have the right to
    refrain from any or all of such activities except to the extent
    that such right may be affected by an agreement requiring
    membership in a labor organization as a condition of employment as
    authorized in section 158(a)(3) of this title.