This question arose due to the California initiative in 1999 (I think), which restricted marriage to unions between men and women. The LDS church supported the initiative, but a number of people opposed it, claiming things such as it would violate the U.S. Constitution (if other states legalized homosexual marriages) due to the requirement of recognizing the public acts of other states.

Not exactly a uniquely Mormon topic (many other religious groups also supported the initiative), but I did a little research, and I'll present my results here.

I gleaned this information from talking to a friend of mine who is a lawyer. The potential problem with such a law is that it seems to violate the US Constitution "full faith & credit" section, which requires states to honor each other's public acts (Article 4, Section 1).

Here is what I gleaned from my friend.

As far as I understand it, there is something called the "public policy exception" to the "full faith and credit" section to the Constitution.

An exception to this section is permitted if honoring a sister state's marriage (or presumably other act) would violate an important public policy of the enforcing state.

According to my friend, the public policy exception has been applied to deny credit to marriages involving incest, interracial unions, bigamy and polygamy, and underaged or mentally incompetent parties.

A reference (review article, I think) for the preceding is: 97 Columbia L.R. 1435. In that article, citations are given for the actual cases described above, which I believe are all separate cases, in

different years (i.e., the interracial ban would not hold up today, as far as I know).

That being said, refusing to recognize homosexual marriages would certainly not be an "open and shut" example of the public policy exception, but it may well be. If challenged, it seems like the case would most likely go to the Supreme Court.

My friend also said there is some stuff in this article: 49 Hastings L.J. 175, but since I don't have access to a law library, I don't know what's in it.