It is unlawful for any person except a medical service plan corporation, incorporated in accordance with this chapter, and operating in accordance with this chapter, and operating in accordance with authority from the commissioner or an insurance company properly qualified in this state to write accident, health or disability insurance, to establish, maintain, or operate a medical service plan, or to solicit subscribers to or enter into contracts with respect to a medical service plan. This prohibition, however, shall not be construed as preventing a person from furnishing medical services for the prevention of diseases among the person's employees or from furnishing the medical services as are required under the Workers' Compensation Law, compiled in title 50, chapter 6, and related legislation when the employee is not charged for the services.