The Taft-Hartley Act, also known as the Labor Management Relations Act, addressed unions and engaged in certain types of secondary boycotts. What is a secondary boycott?

A secondary boycott occurs when a union pressures a neutral or secondary employer - one not directly involved in the labor dispute - to cease doing business with the primary employer the union is targeting. The Taft-Hartley Act of 1947 made this practice an unfair labor practice because it extends the economic pressure beyond the direct dispute to uninvolved parties.

Targeting multiple revenue streams of one company describes a broadened primary boycott strategy, not the definition of a secondary boycott which requires involvement of a neutral third party.

Multiple unions acting against one company describes coordinated or sympathy action, not a secondary boycott, which is defined by targeting a neutral third party rather than the number of unions involved.

While close in concept, this choice describes targeting companies that do business with the primary target rather than convincing others to stop doing business with the primary target - the distinction in the correct answer is the direction of the pressure on the neutral party.