Mo. Rev. Stat. § 104.540

104.540. Law creates vested rights — certain contributions may be withheld from benefits and paid over. — 1. All premium payments and deferred compensation provided for under sections 104.320 to 104.540 are hereby made obligations of the state of Missouri. No alteration, amendment, or repeal of sections 104.320 to 104.540 shall affect the then-existing rights of members and beneficiaries, but shall be effective only as to rights which would otherwise accrue hereunder 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 or paid to, any person under the provisions of sections 104.320 to 104.540 shall not be subject to execution, garnishment, attachment, writ of sequestration, or any other process or claim whatsoever, and shall be unassignable, except with regard to the collection of child support or maintenance, and except that a beneficiary may assign life insurance proceeds. Any retired member of the system may request the executive director of the system, in writing, to withhold and pay on his behalf to the proper person, from each of his monthly retirement benefit payments, if the payment is large enough, the contribution due from the retired member to any group providing state-sponsored life or medical insurance and to the Missouri state employees charitable campaign.

3. The executive director of the system shall, when requested in writing by a retired member, withhold and pay over the funds authorized in subsection 2 of this section until such time as the request to do so is revoked by the death or written revocation of the retired member.

(L. 1957 p. 706 § 23, A.L. 1959 S.B. 274, A.L. 1965 p. 226, A.L. 1981 H.B. 835, et al., A.L. 1988 H.B. 1643 & 1399, A.L. 1992 S.B. 499, et al., A.L. 1998 S.B. 910, A.L. 2002 H.B. 1455, A.L. 2009 H.B. 210)