If your organization has individuals that do not want to be on the group health insurance plan they may refuse coverage. Insurance companies do require that 80% of the employees of an organization enroll in the group plan. If less than that choose to enroll the insurance company will decline to quote the group.
Those that “refuse” the group coverage must sign a “Refusal Form” or statement. The insurance company requires this and of course those that sign the “Refusal” form can not later apply for group coverage. Insurance companies do this to protect themselves from having people elect to enroll in the group coverage once they have a major medical condition.