Mo. Rev. Stat. § 536.014: Rules invalid, when.

No department, agency, commission or board rule shall be valid in the event that:

(1) There is an absence of statutory authority for the rule or any portion thereof; or

(2) The rule is in conflict with state law; or

(3) The rule is so arbitrary and capricious as to create such substantial inequity as to be unreasonably burdensome on persons affected.