29 U.S.C. § 158 : US Code - Section 158: Unfair labor practices

    (a) Unfair labor practices by employer
      It shall be an unfair labor practice for an employer - 
        (1) to interfere with, restrain, or coerce employees in the
      exercise of the rights guaranteed in section 157 of this title;
        (2) to dominate or interfere with the formation or
      administration of any labor organization or contribute financial
      or other support to it: Provided, That subject to rules and
      regulations made and published by the Board pursuant to section
      156 of this title, an employer shall not be prohibited from
      permitting employees to confer with him during working hours
      without loss of time or pay;
        (3) by discrimination in regard to hire or tenure of employment
      or any term or condition of employment to encourage or discourage
      membership in any labor organization: Provided, That nothing in
      this subchapter, or in any other statute of the United States,
      shall preclude an employer from making an agreement with a labor
      organization (not established, maintained, or assisted by any
      action defined in this subsection as an unfair labor practice) to
      require as a condition of employment membership therein on or
      after the thirtieth day following the beginning of such
      employment or the effective date of such agreement, whichever is
      the later, (i) if such labor organization is the representative
      of the employees as provided in section 159(a) of this title, in
      the appropriate collective-bargaining unit covered by such
      agreement when made, and (ii) unless following an election held
      as provided in section 159(e) of this title within one year
      preceding the effective date of such agreement, the Board shall
      have certified that at least a majority of the employees eligible
      to vote in such election have voted to rescind the authority of
      such labor organization to make such an agreement: Provided
      further, That no employer shall justify any discrimination
      against an employee for nonmembership in a labor organization (A)
      if he has reasonable grounds for believing that such membership
      was not available to the employee on the same terms and
      conditions generally applicable to other members, or (B) if he
      has reasonable grounds for believing that membership was denied
      or terminated for reasons other than the failure of the employee
      to tender the periodic dues and the initiation fees uniformly
      required as a condition of acquiring or retaining membership;
        (4) to discharge or otherwise discriminate against an employee
      because he has filed charges or given testimony under this
      subchapter;
        (5) to refuse to bargain collectively with the representatives
      of his employees, subject to the provisions of section 159(a) of
      this title.
    (b) Unfair labor practices by labor organization
      It shall be an unfair labor practice for a labor organization or
    its agents - 
        (1) to restrain or coerce (A) employees in the exercise of the
      rights guaranteed in section 157 of this title: Provided, That
      this paragraph shall not impair the right of a labor organization
      to prescribe its own rules with respect to the acquisition or
      retention of membership therein; or (B) an employer in the
      selection of his representatives for the purposes of collective
      bargaining or the adjustment of grievances;
        (2) to cause or attempt to cause an employer to discriminate
      against an employee in violation of subsection (a)(3) of this
      section or to discriminate against an employee with respect to
      whom membership in such organization has been denied or
      terminated on some ground other than his failure to tender the
      periodic dues and the initiation fees uniformly required as a
      condition of acquiring or retaining membership;
        (3) to refuse to bargain collectively with an employer,
      provided it is the representative of his employees subject to the
      provisions of section 159(a) of this title;
        (4)(i) to engage in, or to induce or encourage any individual
      employed by any person engaged in commerce or in an industry
      affecting commerce to engage in, a strike or a refusal in the
      course of his employment to use, manufacture, process, transport,
      or otherwise handle or work on any goods, articles, materials, or
      commodities or to perform any services; or (ii) to threaten,
      coerce, or restrain any person engaged in commerce or in an
      industry affecting commerce, where in either case an object
      thereof is - 
          (A) forcing or requiring any employer or self-employed person
        to join any labor or employer organization or to enter into any
        agreement which is prohibited by subsection (e) of this
        section;
          (B) forcing or requiring any person to cease using, selling,
        handling, transporting, or otherwise dealing in the products of
        any other producer, processor, or manufacturer, or to cease
        doing business with any other person, or forcing or requiring
        any other employer to recognize or bargain with a labor
        organization as the representative of his employees unless such
        labor organization has been certified as the representative of
        such employees under the provisions of section 159 of this
        title: Provided, That nothing contained in this clause (B)
        shall be construed to make unlawful, where not otherwise
        unlawful, any primary strike or primary picketing;
          (C) forcing or requiring any employer to recognize or bargain
        with a particular labor organization as the representative of
        his employees if another labor organization has been certified
        as the representative of such employees under the provisions of
        section 159 of this title;
          (D) forcing or requiring any employer to assign particular
        work to employees in a particular labor organization or in a
        particular trade, craft, or class rather than to employees in
        another labor organization or in another trade, craft, or
        class, unless such employer is failing to conform to an order
        or certification of the Board determining the bargaining
        representative for employees performing such work:

      Provided, That nothing contained in this subsection shall be
      construed to make unlawful a refusal by any person to enter upon
      the premises of any employer (other than his own employer), if
      the employees of such employer are engaged in a strike ratified
      or approved by a representative of such employees whom such
      employer is required to recognize under this subchapter: Provided
      further, That for the purposes of this paragraph (4) only,
      nothing contained in such paragraph shall be construed to
      prohibit publicity, other than picketing, for the purpose of
      truthfully advising the public, including consumers and members
      of a labor organization, that a product or products are produced
      by an employer with whom the labor organization has a primary
      dispute and are distributed by another employer, as long as such
      publicity does not have an effect of inducing any individual
      employed by any person other than the primary employer in the
      course of his employment to refuse to pick up, deliver, or
      transport any goods, or not to perform any services, at the
      establishment of the employer engaged in such distribution;
        (5) to require of employees covered by an agreement authorized
      under subsection (a)(3) of this section the payment, as a
      condition precedent to becoming a member of such organization, of
      a fee in an amount which the Board finds excessive or
      discriminatory under all the circumstances. In making such a
      finding, the Board shall consider, among other relevant factors,
      the practices and customs of labor organizations in the
      particular industry, and the wages currently paid to the
      employees affected;
        (6) to cause or attempt to cause an employer to pay or deliver
      or agree to pay or deliver any money or other thing of value, in
      the nature of an exaction, for services which are not performed
      or not to be performed; and
        (7) to picket or cause to be picketed, or threaten to picket or
      cause to be picketed, any employer where an object thereof is
      forcing or requiring an employer to recognize or bargain with a
      labor organization as the representative of his employees, or
      forcing or requiring the employees of an employer to accept or
      select such labor organization as their collective bargaining
      representative, unless such labor organization is currently
      certified as the representative of such employees:
          (A) where the employer has lawfully recognized in accordance
        with this subchapter any other labor organization and a
        question concerning representation may not appropriately be
        raised under section 159(c) of this title,
          (B) where within the preceding twelve months a valid election
        under section 159(c) of this title has been conducted, or
          (C) where such picketing has been conducted without a
        petition under section 159(c) of this title being filed within
        a reasonable period of time not to exceed thirty days from the
        commencement of such picketing: Provided, That when such a
        petition has been filed the Board shall forthwith, without
        regard to the provisions of section 159(c)(1) of this title or
        the absence of a showing of a substantial interest on the part
        of the labor organization, direct an election in such unit as
        the Board finds to be appropriate and shall certify the results
        thereof: Provided further, That nothing in this subparagraph
        (C) shall be construed to prohibit any picketing or other
        publicity for the purpose of truthfully advising the public
        (including consumers) that an employer does not employ members
        of, or have a contract with, a labor organization, unless an
        effect of such picketing is to induce any individual employed
        by any other person in the course of his employment, not to
        pick up, deliver or transport any goods or not to perform any
        services.

        Nothing in this paragraph (7) shall be construed to permit any
      act which would otherwise be an unfair labor practice under this
      subsection.
    (c) Expression of views without threat of reprisal or force or
      promise of benefit
      The expressing of any views, argument, or opinion, or the
    dissemination thereof, whether in written, printed, graphic, or
    visual form, shall not constitute or be evidence of an unfair labor
    practice under any of the provisions of this subchapter, if such
    expression contains no threat of reprisal or force or promise of
    benefit.
    (d) Obligation to bargain collectively
      For the purposes of this section, to bargain collectively is the
    performance of the mutual obligation of the employer and the
    representative of the employees to meet at reasonable times and
    confer in good faith with respect to wages, hours, and other terms
    and conditions of employment, or the negotiation of an agreement,
    or any question arising thereunder, and the execution of a written
    contract incorporating any agreement reached if requested by either
    party, but such obligation does not compel either party to agree to
    a proposal or require the making of a concession: Provided, That
    where there is in effect a collective-bargaining contract covering
    employees in an industry affecting commerce, the duty to bargain
    collectively shall also mean that no party to such contract shall
    terminate or modify such contract, unless the party desiring such
    termination or modification - 
        (1) serves a written notice upon the other party to the
      contract of the proposed termination or modification sixty days
      prior to the expiration date thereof, or in the event such
      contract contains no expiration date, sixty days prior to the
      time it is proposed to make such termination or modification;
        (2) offers to meet and confer with the other party for the
      purpose of negotiating a new contract or a contract containing
      the proposed modifications;
        (3) notifies the Federal Mediation and Conciliation Service
      within thirty days after such notice of the existence of a
      dispute, and simultaneously therewith notifies any State or
      Territorial agency established to mediate and conciliate disputes
      within the State or Territory where the dispute occurred,
      provided no agreement has been reached by that time; and
        (4) continues in full force and effect, without resorting to
      strike or lock-out, all the terms and conditions of the existing
      contract for a period of sixty days after such notice is given or
      until the expiration date of such contract, whichever occurs
      later:

    The duties imposed upon employers, employees, and labor
    organizations by paragraphs (2) to (4) of this subsection shall
    become inapplicable upon an intervening certification of the Board,
    under which the labor organization or individual, which is a party
    to the contract, has been superseded as or ceased to be the
    representative of the employees subject to the provisions of
    section 159(a) of this title, and the duties so imposed shall not
    be construed as requiring either party to discuss or agree to any
    modification of the terms and conditions contained in a contract
    for a fixed period, if such modification is to become effective
    before such terms and conditions can be reopened under the
    provisions of the contract. Any employee who engages in a strike
    within any notice period specified in this subsection, or who
    engages in any strike within the appropriate period specified in
    subsection (g) of this section, shall lose his status as an
    employee of the employer engaged in the particular labor dispute,
    for the purposes of sections 158, 159, and 160 of this title, but
    such loss of status for such employee shall terminate if and when
    he is reemployed by such employer. Whenever the collective
    bargaining involves employees of a health care institution, the
    provisions of this subsection shall be modified as follows:
        (A) The notice of paragraph (1) of this subsection shall be
      ninety days; the notice of paragraph (3) of this subsection shall
      be sixty days; and the contract period of paragraph (4) of this
      subsection shall be ninety days.
        (B) Where the bargaining is for an initial agreement following
      certification or recognition, at least thirty days' notice of the
      existence of a dispute shall be given by the labor organization
      to the agencies set forth in paragraph (3) of this subsection.
        (C) After notice is given to the Federal Mediation and
      Conciliation Service under either clause (A) or (B) of this
      sentence, the Service shall promptly communicate with the parties
      and use its best efforts, by mediation and conciliation, to bring
      them to agreement. The parties shall participate fully and
      promptly in such meetings as may be undertaken by the Service for
      the purpose of aiding in a settlement of the dispute.
    (e) Enforceability of contract or agreement to boycott any other
      employer; exception
      It shall be an unfair labor practice for any labor organization
    and any employer to enter into any contract or agreement, express
    or implied, whereby such employer ceases or refrains or agrees to
    cease or refrain from handling, using, selling, transporting or
    otherwise dealing in any of the products of any other employer, or
    to cease doing business with any other person, and any contract or
    agreement entered into heretofore or hereafter containing such an
    agreement shall be to such extent unenforcible (!1) and void:
    Provided, That nothing in this subsection shall apply to an
    agreement between a labor organization and an employer in the
    construction industry relating to the contracting or subcontracting
    of work to be done at the site of the construction, alteration,
    painting, or repair of a building, structure, or other work:
    Provided further, That for the purposes of this subsection and
    subsection (b)(4)(B) of this section the terms "any employer", "any
    person engaged in commerce or an industry affecting commerce", and
    "any person" when used in relation to the terms "any other
    producer, processor, or manufacturer", "any other employer", or
    "any other person" shall not include persons in the relation of a
    jobber, manufacturer, contractor, or subcontractor working on the
    goods or premises of the jobber or manufacturer or performing parts
    of an integrated process of production in the apparel and clothing
    industry: Provided further, That nothing in this subchapter shall
    prohibit the enforcement of any agreement which is within the
    foregoing exception.

    (f) Agreement covering employees in the building and construction
      industry
      It shall not be an unfair labor practice under subsections (a)
    and (b) of this section for an employer engaged primarily in the
    building and construction industry to make an agreement covering
    employees engaged (or who, upon their employment, will be engaged)
    in the building and construction industry with a labor organization
    of which building and construction employees are members (not
    established, maintained, or assisted by any action defined in
    subsection (a) of this section as an unfair labor practice) because
    (1) the majority status of such labor organization has not been
    established under the provisions of section 159 of this title prior
    to the making of such agreement, or (2) such agreement requires as
    a condition of employment, membership in such labor organization
    after the seventh day following the beginning of such employment or
    the effective date of the agreement, whichever is later, or (3)
    such agreement requires the employer to notify such labor
    organization of opportunities for employment with such employer, or
    gives such labor organization an opportunity to refer qualified
    applicants for such employment, or (4) such agreement specifies
    minimum training or experience qualifications for employment or
    provides for priority in opportunities for employment based upon
    length of service with such employer, in the industry or in the
    particular geographical area: Provided, That nothing in this
    subsection shall set aside the final proviso to subsection (a)(3)
    of this section: Provided further, That any agreement which would
    be invalid, but for clause (1) of this subsection, shall not be a
    bar to a petition filed pursuant to section 159(c) or 159(e) of
    this title.
    (g) Notification of intention to strike or picket at any health
      care institution
      A labor organization before engaging in any strike, picketing, or
    other concerted refusal to work at any health care institution
    shall, not less than ten days prior to such action, notify the
    institution in writing and the Federal Mediation and Conciliation
    Service of that intention, except that in the case of bargaining
    for an initial agreement following certification or recognition the
    notice required by this subsection shall not be given until the
    expiration of the period specified in clause (B) of the last
    sentence of subsection (d) of this section. The notice shall state
    the date and time that such action will commence. The notice, once
    given, may be extended by the written agreement of both parties.