Final answer:
The technique most closely associated with the growth of labor unions is Collective bargaining. It is a process of negotiations between workers' unions and employers to establish favorable employment conditions.
Step-by-step explanation:
Among the options given, the technique most closely associated with the growth of labor unions is D) Collective bargaining. This process is fundamental to union activity as it involves negotiation between the union, representing the workers, and the employer to reach a mutually agreeable set of terms and conditions for the workforce. This includes discussions on wages, work hours, benefits, and other employment conditions. Unlike price fixing, protective tariffs, or vertical integration, which are economic strategies used by businesses, collective bargaining is the primary method by which unions exert their influence and advocate for the interests of their members in the labor market. Collective bargaining has been crucial in improving work conditions and compensations for union members when compared to non-union workers. The capacity to negotiate as a group empowers workers and provides a counterbalance to the power of employers, establishing a bilateral monopoly where both the supplier (workers) and buyer (employers) have significant market power.