South carolina constitution
Article XVII: miscellaneous matters
Section 15

A marriage between one man and one woman is the only lawful domestic union that shall be valid or recognized in this State. This State and its political subdivisions shall not create a legal status, right, or claim respecting any other domestic union, however denominated. This State and its political subdivisions shall not recognize or give effect to a legal status, right, or claim created by another jurisdiction respecting any other domestic union, however denominated. Nothing in this section shall impair any right or benefit extended by the State or its political subdivisions other than a right or benefit arising from a domestic union that is not valid or recognized in this State. This section shall not prohibit or limit parties, other than the State or its political subdivisions, from entering into contracts or other legal instruments.