In United States v. Windsor, 133 S. Ct. 2675, the Supreme Court ruled that §3 of DOMA (defining marriage as between one man and one woman for all federal purposes) was unconstitutional.  As discussed in his dissent, Justice Scalia noted that the decision left unresolved many choice-of-law issues.  Justice Scalia noted that it was uncertain whether a same-sex married couple that was married in New York, but who reside in Alabama would be considered married for federal purposes.

On August 29, 2013, the IRS provided guidance in Rev. Rul. 2013-17, 2013-38 I.R.B. __. Pursuant to Rev. Rul. 2013-17, the IRS will recognize a marriage of same-sex individuals that was validly entered into in a state (which includes, for Rev. Rul. 2013-7 purposes, any domestic or foreign jurisdiction with legal authority to sanction marriages) whose laws authorize the marriage of two individuals of the same sex even if the married couple is domiciled in a state that does not recognize the validity of same-sex marriages. Further, the IRS ruled that where the Code or regulations use the terms “spouse,” “husband and wife,” “husband,” and “wife,” such terms shall include an individual married to a person of the same sex if the individuals are lawfully married under state law, and the term “marriage” includes such a marriage between individuals of the same sex.  Finally, the IRS ruled that individuals (whether of the opposite sex or the same sex) who have entered into a registered domestic partnership, civil union, or other similar formal relationship recognized under state law that is not denominated as a marriage under the laws of that state will not be considered “married” for federal tax purposes.

Rev. Rul. 2013-17 states that the IRS will apply these rulings prospectively as of September 16, 2013 but notes that taxpayers may rely on the rulings in filing amended or adjusted returns and refund or credit claims resulting from the rulings to the extent the §6511 statute of limitations has not expired.

It should be noted that the IRS's position is mandatory, which means that same-sex married couples living in states which ban same-sex marriages do not have choice, i.e., they must file as either married filing jointly or married filing separately.  They will not be allowed to file as single.  If a same-sex married couple files as "single" the IRS should challenge that decision.

It is doubtful Rev. Rul. 2013-17 will be the last word on this issue.  In a sense, the IRS completely ignored §2 of DOMA, which generally provides that states are not required to recognize same-sex marriages performed in other states.  Of course, finding someone with standing to challenge the IRS's position will be difficult.  Perhaps a same-sex married couple living in a state that bans same-sex marriage may challenge the IRS's position if it imposes enough of a "marriage penalty" on that couple, however, that is doubtful.  It might also be challenged in the employer plan context as illustrated by the case of Cozen O’Connor v. Tobits, No. 11-0045 (E.D. Pa. 7/29/13), whereby a same-sex widow or widower residing in a state that bans same-sex marriages makes a claim on ERISA pension or life insurance benefits.

There is also the possibility that if a Republican is elected president in 2016, his or her administration may issue a Revenue Ruling which comes to the opposite conclusion.

Eventually, it seems that the Supreme Court will have to address this issue.  Of course, there are several cases across the country that are challenging same-sex marriage bans.  The entire issue could be rendered moot if the Supreme Court rules that these bans are unconstitutional.