Mo. Rev. Stat. § 287.730

Wherever the employer carries his risk or whatever substitute schemes for insurance provided for in section 287.370 have been approved, the division shall inform the director of the department of commerce and insurance, who, thereupon, shall assess and in like manner a similar tax shall be collected from the employer carrying his own risk at the same rate and on the same basis as taxes are assessed against insurance carriers, of any character, carrying like risks in this state under the provisions of this chapter.