S.C. Code Ann. § 41-7-30: Labor organization membership as condition of employment.

(A) It is unlawful for an employer to require an employee, as a condition of employment, or of continuance of employment to:

(1) be or become or remain a member or affiliate of a labor organization or agency;

(2) abstain or refrain from membership in a labor organization; or

(3) pay any fees, dues, assessments, or other charges or sums of money to a person or organization.

(B) It is unlawful for a person or a labor organization to directly or indirectly participate in an agreement, arrangement, or practice that has the effect of requiring, as a condition of employment, that an employee be, become, or remain a member of a labor organization or pay to a labor organization any dues, fees, or any other charges; such an agreement is unenforceable.

(C) It is unlawful for a person or a labor organization to induce, cause, or encourage an employer to violate a provision of this section.