Miss. Code § 77-5-719
After the creation of a joint agency, any other municipality may become a member thereof upon application to such joint agency after the adoption of a resolution by the utility commission of the municipality setting forth the determination and finding prescribed in Section 75-5-717, and the adoption by the governing authorities of the municipality of a resolution or ordinance ratifying the determination of the utility commission and authorizing said municipality to participate, and with the unanimous consent of the members of the joint agency evidenced by the resolutions of their respective utility commissions. Any municipality may withdraw from a joint agency, provided, however, that all contractual rights acquired and obligations incurred while a municipality was a member shall remain in full force and effect.
Miss. Code § 77-5-719