S.C. Code § 54-5-30
The election for the commissioners of the port utilities commission of such cities may be held in the following manner: Upon the duly signed petition of registered electors qualified to vote in such cities equal in number to twenty-five per cent of the votes cast for all candidates for mayor at the last preceding city election of such city, showing the residence and occupation of each petitioner, the mayor shall, by proclamation, order a special election to be held at a time specified in such proclamation, not later than two months and not earlier than two weeks after such petition shall be duly filed with the proper officer. Those entitled to vote at such special election shall be all those who are then duly qualified registered electors of such cities. Such special election shall be held and conducted as is provided by law for the conduct of municipal elections.
S.C. Code § 54-5-30