An appeals court in New York has ruled that a United States law defining marriage as a union between a man and a woman is unconstitutional.
The 2nd Circuit Court of Appeals said the law denies federal benefits to lawfully married same-sex couples.
The Defense of Marriage Act was passed in 1996. Since then, six states have legalized same-sex marriage but, because of the 1996 law, the federal government does not recognize same-sex marriages performed in those states, Reuters reports.
The case was brought by Edith Windsor, 83, who married her partner Thea Clara Spyer in Canada in 2007.
Ms Spyer died in 2009 of multiple sclerosis, leaving all of her property to Windsor. Because the marriage was not recognized under federal law, Windsor had to pay more than $363,000 in federal estate taxes, according to her lawsuit.
Windsor's attorneys argued that the act violates the 14th Amendment of the U. Constitution, which guarantees equal protection under the law.
A federal court in New York agreed, and the ruling by the 2nd Circuit on Thursday upheld the lower court decision.
It is the second federal appeals court to reject a portion of the law.
The same-sex marriage issue could be taken up by the US Supreme Court in its current term.