On August 29, 2013, the Internal Revenue Service (IRS) released guidance regarding the federal tax treatment of same-sex spouses. In Revenue Ruling 2013-17, the IRS clarified that it will consider a same-sex couple to be married for federal tax purposes if they were legally married in a state or foreign country that recognizes same-sex marriage, regardless of where the couple resides.  Essentially, this new IRS guidance grants favorable tax treatment to all married couples, regardless of how their local state law treats same-sex marriage.  The IRS also released a detailed set of FAQs addressing various tax implications for same-sex couples, which include information on how individuals may file amended income tax returns and how employers may file amended employment tax returns for refunds of excess taxes paid during any tax year that has not “closed” due to the expiration of the applicable statute of limitations for applying for tax refunds.  Regarding qualified retirement plans, as of September 16, 2013, all qualified retirement plans (e.g., 401(k) plans, profit sharing plans, etc.) must treat a same-sex spouse as a “spouse” for purposes of satisfying federal tax laws relating to qualified retirement plans.  Additional guidance is expected related to the application of this new rule to health and welfare plans, including whether this new rule may be applied retroactively and the timing of any plan amendments.  Finally, the IRS also issued a set of FAQs regarding domestic partners and civil-union partners which state that the IRS does not recognize civil unions or registered domestic partners as being “married” for federal tax purposes.  Employers should continue to watch for further guidance relating to the federal tax implications of providing same-sex employee benefits, including any information from state and local tax authorities.