Mo. Rev. Stat. § 144.500

If fraud or evasion on the part of a person is discovered by the director of revenue, he shall determine the amount of which the state has been defrauded, shall add to the amount so determined a penalty equal to twenty-five percent thereof, and shall assess the same against the person. The amount so assessed shall be immediately due and payable; provided, however, that the director of revenue shall promptly thereafter give to said person written notice of such assessment and penalty, which notice shall be served personally on such person, or by registered mail. Such person shall have the right to petition for hearing of such assessment, as is provided herein.