Mo. Rev. Stat. § 104.250: Law creates vested rights — benefits exempt from taxes and executions — exception, subject to child support and spousal maintenance.

1. All payroll deductions and deferred compensation provided for under sections 104.010 to 104.270 are hereby made obligations of the state of Missouri. No alteration, amendment, or repeal of sections 104.010 to 104.270 shall affect the then existing rights of members and beneficiaries, but shall be effective only as to rights which would otherwise accrue under sections 104.010 to 104.270 as a result of services rendered by an employee after such alteration, amendment, or repeal.

2. Any annuity, benefits, funds, property, or rights created by, or accruing to, any person under the provisions of sections 104.010 to 104.270 are hereby made and declared exempt from any tax of the state of Missouri or any political subdivision or taxing body thereof, and shall not be subject to execution, garnishment, attachment, writ of sequestration, or any other process or claim whatsoever, and shall be unassignable except that any payment from the retirement system shall be subject to the collection of child support or spousal maintenance.