FMLA defines spouse according to state law

A: The FMLA allows an otherwise eligible employee to take leave to care for a spouse with a serious health condition. When determining who is a “spouse,” the FMLA looks to the law of the state where the employee resides, which includes common law marriages and same-sex marriages, where they are recognized by state law. If this employee’s “partner” is his spouse under state law, then he is entitled to FMLA leave if he is otherwise eligible (i.e. has worked for at least 1,250 hours, has been employed for at least 12 months, and is employed at a worksite with at least 50 employees within 75 miles). If you are uncertain whether the employee is married to his partner, you have the right to ask. When it comes to leave to bond with the newborn child, or to care for the child if it has a serious health condition, the FMLA only applies once the child is actually born (see Lukudu v. JBS USA, LLC, WD Ky, March 2014). If you are unsure if the FMLA applies to a given situation, contact your Vigilant staff representative. Also check out our Legal Guide, “FMLA: Eligibility Requirements” (3128).