S.C. Code § 9-1-640
Notwithstanding any other provisions of law governing the System, effective July 1, 1964, there shall be two classes of participating employers and two classes of members. Class One employers shall include all employers who irrevocably elect, by written notification to the Board not later than December 31, 1964, to remain, and to have members in their employ remain, under the provisions of the System as in effect on June 30, 1964. Class Two employers shall include all employers who irrevocably elect, by written notification to the Board not later than December 31, 1964, to participate, and to have members in their employ participate, under the provisions of the System as amended effective July 1, 1964. Any such notification shall become effective for all purposes as of July 1, 1964. Failure by any employer to file such notification shall be deemed an irrevocable election by the employer to be a Class One employer. In any event, the State shall be a Class Two employer. Members in the employ of a Class One employer shall be Class One members, and members in the employ of a Class Two employer shall be Class Two members. Any employer becoming such on or after July 1, 1964 shall be a Class Two employer. In the event that a member shall transfer, without break in membership, from one class to another, the Board shall determine his benefit upon retirement in an equitable manner by uniform rules consistent herewith.
Notwithstanding the foregoing, any Class One employer may elect to become a Class Two employer and have employees in its employ participate under the provisions of the System as amended effective July 1, 1964; provided, that such employer and each and every such member shall make such additional contributions to the System, plus regular interest, as would have been required had such employer become a Class Two employer as of July 1, 1964.
Effective July 1, 1976, or any subsequent July first, a Class One employer may elect Class Two coverage on July 1, 1976, or as of July first of any year thereafter. It is mandatory for each Class One employee of any such employer to participate in Class Two coverage from the effective date of the employer election. Upon service retirement, a member shall receive a service retirement allowance equal to the sum of his benefit computed by the Class One formula for service credited under Class One membership and his benefit computed by the Class Two formula for service credited under Class Two membership. A Class One member may convert Class One service to Class Two by paying into the System two and one-half percent of his earnable compensation, or the average of the highest twelve consecutive quarters, whichever is greater, for each year prorated for periods of less than one year. A member who elects to convert from Class One to Class Two must convert all such service for which eligible.
S.C. Code § 9-1-640