A health maintenance organization shall not exclude part-time employees or refuse to offer the same benefits to part-time employees as it offers to the employee groups of which the part-time employees would be members if they were full-time employees. The insurer shall offer to include the part-time employees as part of the employer's employee group, at the full rate to be paid by the employer, at a rate prorated between the employer and the employee or at the employee's expense. "Part-time employee" means any employee who works a minimum of at least 17 1/2 hours per week. (Added 1989, No. 34, § 4.)