Mass. Gen. Laws ch. 149, § 20B: Liability for unlawful acts of officers, members or agents of an organization

Section 20B. No officer or member of any association or organization, and no association or organization, participating or interested in a labor dispute, as defined in section twenty C, shall be held responsible or liable in any court for the unlawful acts of individual officers, members or agents, except upon clear proof of actual participation in, or actual authorization of, such acts, or of ratification of such acts after actual knowledge thereof.