S.C. Code § 9-1-1960
Effective July 1, 1972, any member of the General Assembly who has retired or may retire under the provisions of the South Carolina Retirement Act and has twenty or more years of creditable service shall be paid in the same manner as provided in Section 9-1-1910 a monthly sum in addition to the retirement allowance he may receive under such act, to provide him a gross minimum of one hundred and fifty dollars per month, plus one dollar per month for each completed year of such service in excess of twenty years. Should such member of the General Assembly elect to receive a reduced retirement allowance as provided in such act, he shall be paid under the provisions of this section only such amount as would be paid under this section had he not elected such optional allowance.
S.C. Code § 9-1-1960