It shall be unlawful to cause or threaten to cause, and/or combine or conspire to cause or threaten to cause, injury to one not a party to the particular labor dispute, to aid which such boycott is initiated or continued, whether by (a) withholding patronage, labor, or other beneficial business intercourse; (b) picketing; (c) refusing to handle, install, use or work on particular materials, equipment or supplies; or (d) by any other means, in order to bring him against his will into a concerted plan to coerce or inflict damage upon another or to compel the party with whom such labor dispute exists to comply with any particular demands.