Mo. Rev. Stat. § 86.1430
The right of any person to pension or pensions, to the return of contributions, disability or death benefits, or any other right accrued or accruing to any person under the provisions of sections 86.1310 to 86.1640 and the moneys in the various funds created under sections 86.1310 to 86.1640 shall not be subject to execution, garnishment, attachment, or any other process whatsoever and shall be unassignable except as specifically provided in sections 86.1310 to 86.1640, and except for court orders or assignments approved by a court to provide support for family members or a former spouse of any person entitled to benefits under sections 86.1310 to 86.1640. The moneys in the various funds created under sections 86.1310 to 86.1640 are hereby exempt from any tax of the state of Missouri or of any municipality or political subdivision thereof. A revocable request or authorization by a member or a beneficiary to withhold and apply for the requester's convenience some portion or all of a benefit payment shall not be deemed an assignment prohibited under this section provided that any such request shall remain revocable at all times except as to payments or withholdings effected prior to any such revocation. The retirement system may, but shall not be obligated to, comply with any such request.
§ 86.1430, RSMo