27 Miss. Code. R. 210-10-101
Employee contributions shall be made on the basis of the contribution rates as set by the Board of Trustees from time to time as applied to earned compensation as defined by law.
Deductions for Article II, [now Article III beginning at Miss. Code Ann. § 25-11-101 et seq. (1972, as amended)], from the salary of school employees employed for the school year shall be made on the basis of earned annual compensation less $1200 per year, payable monthly on a pro-rata basis. Example: A teacher having a contract for $1600 for the school year of 8 months and receiving $200 per month would not pay on the first $150 per month of her salary, as she has only an 8 months contract and 8 x $150 = $1200. She would therefore contribute 4[CENT] of $200 minus $150, or 4[CENT] of $50 per month or $2 per month to Article II, [now Article III beginning at Miss. Code Ann. § 25-11-101 et seq. (1972, as amended)]. However, if she works in other public employment the other 4 months during the year, she would pay 4[CENT] of her total salary for these months as she will get her $1200 exemption from her school service.
Effective July 1, 1968, deductions for employee contributions from the salaries of all employees for retirement annuity coverage shall be based on all covered wages not to exceed the statutory limits.
27 Miss. Code. R. 210-10-101