Mo. Rev. Stat. § 290.305
No person, firm or corporation shall violate the wage provisions of any contract contemplated in sections 290.210 to 290.340 or suffer or require any employee to work for less than the rate of wages so fixed, or violate any of the provisions contained in sections 290.210 to 290.340. Where workers are employed and their rate of wages has been determined as provided in sections 290.210 to 290.340, no person, either on his or her behalf or for any other person, shall request, demand or receive, either before or after such worker is engaged, that such worker pay back, return, donate, contribute, or give any part or all of said worker's wages, salary, or thing of value, to any person, upon the statement, representation, or understanding that failure to comply with such request or demand will prevent such worker from procuring or retaining employment, and no person shall, directly or indirectly, pay, request or authorize any other person to violate this section. This section shall not apply to any agent or representative of a duly constituted labor organization acting in the collection of dues or assessments of such organization.
§ 290.305, RSMo