Mo. Rev. Stat. § 379.889
Commercial casualty insurance rates shall not be excessive, inadequate or unfairly discriminatory. No rate shall be held to be excessive unless such rate is unreasonably high for the insurance coverage provided. No rate shall be held to be inadequate unless such rate is unreasonably low for the insurance coverage provided and is insufficient to sustain projected losses and expenses or unless such rate is unreasonably low for the insurance coverage provided and the use of such rate has, or if continued will have, the effect of destroying competition or creating a monopoly. Unfair discrimination shall be defined to include, but shall not be limited to, the use of rates which unfairly discriminate between risks in the application of like charges or credits or the use of rates which unfairly discriminate between risks having essentially the same hazard.
§ 379.889, RSMo