When is bannering, picketing?

The effectiveness of union tactics depends on many factors. Take for example the bannering and leafletting of businesses to protest some union objective. Thats what the Carpenter's union is doing in this California town. The National Labor Relations Act, since Taft-Hartley, prohibits secondary picketing. Thats where a union targets a customer of the employer with whom the union has a labor dispute. Its illegal to picket a "secondary," and the NLRB can enjoin the activity and a union can be sued for damages.