The Supreme Court has held that the Defense of Marriage Act (“DOMA”) is unconstitutional. DOMA defined “marriage” and “spouse” to the exclusion of same-sex partners for purposes of federal law. As a result, same-sex partners (even those legally married or otherwise legitimized under state law) were not considered married or to be spouses for purposes of federal law, including tax law.

The Supreme Court’s decision in U.S. v. Windsor ends this disparate treatment of same sex couples under federal law. Windsor involved a same-sex couple of over forty years, Edie Windsor and Thea Spyer. Edie and Thea registered as domestic partners in New York City and legally married in Canada. Thea died leaving her estate to Edie. Because their same-sex marriage was not recognized for purposes of federal law under DOMA, Thea’s estate did not qualify for the unlimited marital estate tax deduction and, as a result, the estate had to pay more than $300,000 in federal estate taxes. Edie, as Executor for Thea’s estate, paid this amount and sued for a refund and a declaration that DOMA violated the U.S. Constitution. Yesterday, the Supreme Court agreed with Edie by ruling by a 5 to 4 vote that DOMA is unconstitutional and that the authority to define and regulate marriage lies with the states.

Windsor’s effects are certain to have wide-ranging effects beyond eligibility for the unlimited marital estate tax deduction. Same-sex married couples and state-sanctioned partners should consult legal counsel to identify the effect of the Supreme Court’s decision on them. For example, many couples should consider filing amended gift, estate, and/or income tax returns with claims for a refund.