The ally doctrine refers to the situation when a employer subject to a strike effectively uses the employees of a neutral employer as strike breakers. It allows a union to picket a secondary employer which has become an ally of the primary employer by entering an arrangement under which the ally agrees to assist in the dispute by performing farmed out work.
In strike situations, solidarity action generally is prohibited. The purpose of the ban on solidarity action is designed to insulate innocent third parties from becoming enmeshed in labor disputes in which they have no interest. However, there are exceptions to this prohibition which allow solidarity action to be directed at an 'ally' of the employer in the dispute. Solidarity action may be taken against a company to which work has been transferred as a result of a strike. Courts have generally found that in these situations the secondary employer is not neutral, but someone who has become involved in the primary dispute.
The relationship between the primary and the secondary employer is not based on the fact that some third party is taking on struck work, but rather that the struck work employer is is closely related with the other enterprise as to merge identities; therefore, both constitute the primary employer. However, only where, in addition to common ownership, there is common control of day-to-day operations and labor policies and some integration of operations that two operations will be characterized as a single enterprise and an ally relationship will be found.