Answer:
Nonunion members in a workplace weakened the unions.
Step-by-step explanation:
Closed shop, is a form of arrangement where employers only accept to employ individuals that are a member of a labor or trade union. This employment will be based on the terms and conditions of a labor agreement or contract.
Consequently, the reason some unions prefer a "closed shop" is because, it gives assurance that all workers will follow the regulations of the union, such as participating in strikes, payment of union dues, unified deal agreement with the employers, etc. Otherwise, nonunion members in a workplace weakened the unions.