What characterizes ‘closed shops’ within the context of the ILWU?

The correct choice highlights that closed shops require employers to hire only union members, thereby promoting stronger union membership. In the context of the ILWU, this arrangement ensures that workers must be members of the union to gain employment, which helps maintain and potentially increase the union's size and influence within the workplace.

This characteristic contributes to a unified workforce that is invested in collective bargaining and mutual support, making it easier for the union to negotiate better terms, benefits, and conditions for its members. With a closed shop model, the workforce is aligned in their labor interests, reinforcing solidarity among workers and enhancing the union's bargaining power.

In contrast, the other options describe scenarios that do not align with the concept of a closed shop. For example, greater participation from non-members, workplaces where membership is not necessary, and an emphasis on non-union contract workers reflect open shop or non-union work environments, where union membership is either not required or actively discouraged. This distinction is critical in understanding the function and implications of union contractual practices in workplaces represented by the ILWU.