I own a three-family house, and I've been renting one of the apartments to a woman with two children who is separated from her husband. If he moves in, am I entitled to raise her rent? Can I reject the husband? The lease expired and she never asked for a renewal.

Usually, you wouldn’t be able to hike the rent simply because another person moved in. However, because the lease is no longer in effect, you have some latitude, our experts say.

Assuming this isn’t a rent-regulated unit, you’re “free to do pretty much whatever you like as this is a month to month tenancy,” says real estate attorney Dean Roberts of Norris, McLaughlin & Marcus. “If the tenant were under a lease the addition of another occupant would not normally result in an increase in rent absent a very specific provision within the lease providing for this increase.”

At this point you have two options: continue on a month-to-month basis and raise the rent next month, or “you can offer a renewal lease which may reflect an increase in market rates if applicable,” says Roberta Axelrod, a real estate broker and asset manager at Time Equities.

Just be sure to leave the question of her husband out of it: charging her more because she lives with a partner sounds an awful lot like discrimination based on her marital status, which is illegal, notes Axelrod.

Leigh Kamping-Carder is a senior editor at BrickUnderground.com, the online survival guide to finding a NYC apartment and living happily ever after. To see more expert answers or to ask a real estate question, click here.