This applies even to married gay couples that lives in states that do not recognize their union -- so long as they were married in a state where same-sex marriage is legal.
"Today's ruling provides certainty and clear, coherent tax filing guidance for all legally married same-sex couples nationwide. It provides access to benefits, responsibilities and protections under federal tax law that all Americans deserve," said Secretary Jacob J. Lew in a statement. "This ruling also assures legally married same-sex couples that they can move freely throughout the country knowing that their federal filing status will not change."
The U.S. Treasury and Internal Revenue Service decision comes on the heels of the landmark Supreme Court ruling in June that said same-sex couples are entitled to federal benefits. The ruling struck down the 1996 law blocking federal recognition of gay marriage.
Thirteen states and Washington, D.C., have legalized same-sex marriage as of August 2013: California, Delaware, Connecticut, Iowa, Maine, Maryland, Massachusetts, Washington, Vermont, Rhode Island, New York, Minnesota and New Hampshire.