The legal position of trade unions has continued as uncertain and unsatisfactory to the unions, as if no Clayton Act had been passed.  The closed shop has been condemned as coercion of non-unionists.  Yet in the Coppage case[95] the United States Supreme Court found that it is not coercion when an employer threatens discharge unless union membership is renounced.  Similarly, it is unlawful for union agents to attempt organization, even by peaceful persuasion, when employes have signed contracts not to join the union as a condition of employment.[96] A decision which arouses strong doubt whether the Clayton Act made any change in the status of trade unions was given by the Supreme Court in the recent Duplex Printing case.[97] In this decision the union rested its defense squarely on the immunities granted by the Clayton Act.  Despite this, the injunction was confirmed and the boycott again declared illegal, the court holding that the words “employer and employes” in the Act restrict its benefits only to “parties standing in proximate relation to a controversy,” that is to the employes who are immediately involved in the dispute and not to the national union which undertakes to bring their employer to terms by causing their other members to boycott his goods.

The prevailing judicial interpretation of unlawful union methods is briefly as follows:  Strikes are illegal when they involve defamation, fraud, actual physical violence, threats of physical violence, or inducement of breach of contract.  Boycotts are illegal when they bring third parties into the dispute by threats of strikes, or loss of business, publication of “unfair lists,"[98] or by interference with Interstate commerce.  Picketing is illegal when accompanied by violence, threats, intimidation, and coercion.  In December 1921 the Supreme Court declared mere numbers in groups constituted intimidation and, while admitting that circumstances may alter cases, limited peaceful picketing to one picket at each point of ingress or egress of the plant.[99] In another case the Court held unconstitutional an Arizona statute, which reproduced verbatim the labor clauses of the Clayton Act;[100] this on the ground that concerted action by the union would be illegal if the means used were illegal and therefore the law which operated to make them legal deprived the plaintiff of his property without due process of law.  In June 1922, in the Coronado case, the Court held that unions, although unincorporated, are in every respect like corporations and are liable for damages in their corporate capacity, including triple damages under the Sherman Anti-Trust law, and which may be collected from their funds.