Mo. Rev. Stat. § 87.425

The board of trustees may assess each member of the fire department such sum per month as may be determined by the rules and regulations adopted by the board, and such assessment shall not be increased or diminished during any one fiscal year, the sums so assessed to be deducted and withheld from the monthly pay of each member, and the same to be placed by the treasurer of the board to the credit of the pension fund.