S.C. Code § 58-9-320
When in the judgment of the commission there is a reasonably substantial affiliation of any telephone utility engaged in business in this State with any other corporation or person or when in the judgment of the commission any other corporation or person either exercises, or is in position to exercise, by reason of ownership or control of securities or for any other cause, any reasonably substantial control over the business or policies of any telephone utility engaged in business in this State, the burden of proof shall be upon the telephone utility to establish as determined by the commission the reasonableness, fairness, and absence of injurious effect upon the public interest of any fees or charges growing out of any transactions between any telephone utility and such other corporation or person. Every telephone utility shall be required to produce, if so ordered by the commission, for the information of the commission, the Office of Regulatory Staff, and the public, all such contracts, papers, and documents relating thereto and explanatory thereof as may be required by the commission, and unless the reasonableness, fairness, and absence of injurious effect upon the public interest of such fees and charges are established as determined by the commission, they shall not be allowed by the commission for rate-making purposes. The commission shall not allow for rate-making purposes any fees or expenses included in any contract or agreement with an affiliate representing charges that the commission has directly disallowed in its rate-making orders.
S.C. Code § 58-9-320