The National Labor Relations Act does not specifically prohibit an employer from temporarily locking out his employees during collective bargaining negotiations. For many years, nevertheless, only lockouts used solely to avoid substantial economic loss as a result of union action-so-called "defensive" lockouts-were allowed. However, the emphasis which Congress placed on equality of bargaining pressure in enacting the Taft-Hartley amendments to the NLRA has caused a change in this judicial attitude. Although a few courts have gone so far as to suggest that the lockout should be as freely available as the strike, the United States Supreme Court has been more cautious in defining the legal limits of the lockout. In fact, prior to its decision in American Ship Building v. NLRB, the Court had held only that a non-struck member of a multi-employer bargaining unit could lock his employees out after the union had struck one of the other members of the bargaining group.
Michigan Law Review,
The Unanswered Questions of American Ship,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol64/iss5/8