Most employers generally are aware of their obligations under the Family and Medical Leave Act to grant leave to employees to care for family members. However, FMLA narrowly limits the definition of family member to a “spouse, or a son, daughter or parent, of the employee, if such spouse, son, daughter or parent has a serious health condition.” This definition may appear self-explanatory, but it is further restricted by the U.S. Department of Labor’s interpretive regulations, which set forth additional criteria for determining whether the requested leave is indeed needed to care for the family member.

For the most part, the term “family member” adheres to its ordinarily accepted meaning, but there are exceptions.

FMLA defines “parent” as the biological parent of an employee, or an individual who stood “in loco parentis,” or acted as a parent to an employee, when the employee was a minor. The definition does not include a parent-in-law or grandparent unless the individual stands “in loco parentis” to the requesting employee.

FMLA defines “son or daughter” as a “biological, adopted, or foster child, a stepchild, a legal ward, or a child of a person standing in ‘loco parentis,’ who is under 18 years of age, or 18 years of age or older and incapable of self-care because of a mental or physical disability.”

If a child is younger than 18, you simply need to determine whether the child suffers from a “serious health condition” as defined by FMLA and whether leave is needed to care for the child. If the child is 18 or older, a serious health condition alone will not justify leave; the child also must be incapable of self-care because of a physical or mental disability.

FMLA defines “spouse” as “a husband or wife, as the case may be.” DOL has clarified the ambiguous phrase “as the case may be” by defining spouse to mean “a husband or wife as defined or recognized under State law for purposes of marriage in the State where the employee resides, including common-law marriage in States where it is recognized.”

Legal marital status under applicable state law becomes particularly important when assessing requests for leave to care for same-sex or opposite-sex domestic partners because FMLA does not apply to unmarried domestic partners.

In fact, whether leave must be granted to same-sex partnerships depends on how such unions are treated under the law of the state in which you work. If a state does not recognize same-sex marriages, leave to care for a same-sex partner is not available under FMLA. DOL has received many inquiries regarding FMLA’s application to domestic partners and consistently has responded that FMLA permits the use of leave only to care for a spouse, parent, son or daughter.

However, if your state recognizes same-sex marriages, the leave would qualify under FMLA. An opinion letter from the DOL clarifies that nothing in FMLA supersedes any state or local provision that provides greater family leave rights than under FMLA so that coverage may exist in states that recognize same-sex marriages.

Therefore, consistent with FMLA language, if an employee requests leave to care for a same-sex spouse in a state that recognizes gay marriages, FMLA leave would be available to the employee. Further, by including common-law spouses within FMLA coverage, there may be instances in which a domestic partner is deemed a “spouse” under FMLA by operation of the state’s law regarding recognition of common-law marriage.

Finally, before denying leave, you must verify the state in which an employee was married and whether the state in which the employee works recognizes that marriage. If an employee entered into a common-law or same-sex marriage in another state that allows such unions, the marriage arguably would be valid in those states, as well.

Check your records to see whether an employee who is seeking FMLA leave and claiming a common-law marriage has negated this required element by indicating “single” in employee personnel records, such as benefits election forms. Currently, there are only a dozen or so states that recognize common-law marriages, which typically require a permanent and exclusive agreement to enter into a marriage relationship, cohabitation sufficient to warrant fulfillment of the necessary relationship, and an assumption of marital duties and obligations.

You may extend your FMLA policy to employees so they may care for their domestic partners even though doing so is not required by law. But if you do, keep in mind you still must extend legally required FMLA benefits to the employee to care for himself or herself and covered family members.

The bottom line is you need to pay careful attention to what employees say when discussing need for time off in connection with a family member’s illness. Of course, circumstances will vary, and you must strive to make appropriate leave decisions on a case-by-case basis. And because a number of states have enacted similar leave statutes with analogous, but nonetheless different, provisions to those of FMLA, you must consider them when assessing employee leave requests.

Victoria L. Donati and Jason C. Kim are partners in the employment law group with Chicago-based law firm Neal, Gerber & Eisenberg LLP.