The Supreme Beings should weigh in on this. I'm sure it's in the Constitution somewhere, provided that they say so. Otherwise, it's not.
How would the IRS react?...........
It was landmark U.S. Supreme Court precedent Reynolds v. United States in 1878 that made “separation of church and state” a dubiously legitimate point of case law, but more importantly; it confirmed the Constitutionality in statutory regulation of marriage practices.
(See also: Late Corporation of the Church of Jesus Christ of Latter-Day Saints v. United States, 1890.)
No man can become a law unto himself under the guise of freedom of religion... Marriage is a religious rite, not a civil right...
"We have the right to regulate practice, not belief." (Reynolds)