Final answer:
Work councils are prohibited in the United States primarily because they are seen as competitors to unions.
Step-by-step explanation:
In the United States, work councils are prohibited primarily because they are seen as competitors to unions. Work councils, also known as employee representative bodies, are common in many European countries and serve as a forum for employees and management to discuss work-related issues.
However, in the United States, the role of representing employees in the workplace is typically reserved for labor unions, and therefore work councils are seen as potentially undermining the authority and influence of unions.