Section 5. Any person residing in the commonwealth shall have the right to become a subscriber of a medical service corporation if his qualifications meet those specified in the by-laws of such corporation, provided that such a corporation may, in its discretion, refuse to issue a subscription certificate to, or upon due notice cancel the subscription certificate of, any person who has made any fraudulent claim or representation to the corporation or to a participating physician, participating chiropractor or to any other participating provider of health services licensed under the laws of the commonwealth, or has been guilty of uncooperative or unethical dealings with the corporation, or has failed to pay dues and assessments seasonably and promptly or for any other cause which may be approved by the commissioner. Such corporation shall provide for annual open enrollment periods of not less than two months’ duration. Proper notification shall be given to prospective subscribers in a form subject to approval by the commissioner.