Mo. Rev. Stat. § 104.1039
If a retiree is employed as an employee by a department and works more than one thousand hours per year regardless of the number of positions held on or after the first day of employment, the retiree shall not receive an annuity or additional credited service for any month or part of a month for which the retiree is so employed. The system shall recover any benefit payments received by the retiree during any year that the retiree works more than one thousand hours pursuant to section 104.1060. The term "year" as used in this section shall mean the twelve-month period beginning on the annuity starting date and each subsequent year thereafter.
(L. 1999 S.B. 308 & 314, A.L. 2001 S.B. 371)