United States v Windsor
This case is better known as the case where the US Supreme Court struck down DOMA, or the Defense of Marriage Act. What does this have to do with retirement plans? The Act limited benefits provided to spouses under federal law only to legally married couples that included a man and a woman. Since that time some states have adopted laws that extend marriage to same sex couples. What DOMA said is that these marriages would not be recognized for matters arising from federal law. For example, in a 401(k) plan, if a married participant names someone other than his or her spouse as a beneficiary, then the spouse must consent to that beneficiary or else the designation is not effective. However, DOMA said that if the marriage is between a same sex couple, then the spouse does not get the protection of the law and the participant can name any beneficiary that he or she wants, as if the participant is not married. The Court held that the provision in question violated the equal protection and due process clause of the 5th Amendment. Historically, regulating marriage has been the province of the states. the Constitution does not give that power to the federal government.
With the repeal of DOMA, retirment plans must recognize all legal marriages. In most cases, this is pretty simple. But what happens when a same sex couple gets married in a state permitting this kind of marriage, then moves to a state that does not grant same sex marriages? Does the relocation state recognize a same sex marriage performed in a state where it is legal? These are some lingering questions that the Court did not address. It will be left to trial courts, and maybe even the IRS to provide additional guidance in these less common cases.