There have been a number of cases that have declared that Section 3 of the Defense of Marriage Act is unconstitutional. That provision defines marriage for purposes of administering federal law as the “legal union between one man and one woman as husband and wife.” It further defines “spouse” as “a person of the opposite sex who is a husband or wife.”
See my prior posts here and here.
In a recent FAQ, the IRS has indicated that it will continue to treat same-sex married couples as unmarried individuals for tax provisions that relate to marital status, regardless of these court decisions. The FAQ also provides guidance on which member of the couple can claim a child as a dependent (either one, or if they both claim it, the one with whom the child lived with longer) and adoption expense credits.
Answers to Frequently Asked Questions for Same-Sex Couples