Mo. Rev. Stat. § 339.539: Choosing an appraiser or discriminating against one for membership or lack of membership in appraisal organization prohibited.

No bank, savings and loan association, credit union, mortgage banker or lending institution may exclude a state certified real estate appraiser or state licensed real estate appraiser from consideration for an appraisal assignment or specialized appraisal services by virtue of membership or lack of membership of the state certified real estate appraiser or state licensed real estate appraiser in any particular real estate appraisal organization.