Federal law generally allows a tenant to have a “companion animal,” even if the lease says that no pets are allowed.

Q: I own a duplex, and I rent the two units out to tenants. Both have a strict “no pets” clause in their lease. However, one tenant now has acquired a small dog and says she’s able to keep the pet because her psychologist says the dog is a “companion animal” to help her deal with depression. What can I do?

A: Sorry, but I’m afraid that you probably will have to let the tenant keep her dog despite the “no pets” clause in the rental agreement that she signed.

A growing number of mental-health professionals are recommending that their patients get an “emotional-support” or “companion” animal to cope with their depression or other psychological problems. Much like blind people who must depend on guide dogs, most of these tenants are protected by federal fair-housing laws, even though they often can function physically as well as any other able-bodied person.

Many landlords think that some tenants are abusing the emotional-support-animal provision of the federal law just so they can have a dog, cat or other type of animal in a building where they knew no pets were allowed when they first signed their lease.

Such problems are compounded by the fact that most landlords not only must comply with the nation’s complex set of fair-housing laws, but also must adhere to an equally complicated – and sometimes contradictory – group of rules established by the federal Americans with Disabilities Act of 1990.

Among the dichotomies: While the Fair Housing Act requires property owners to “make reasonable accommodations” for their tenants’ health needs, the Americans with Disabilities Act generally prohibits owners from asking for details about the physical or psychological problems that supposedly require the special accommodations.

This means that if a tenant in a “no-pets” building suddenly requests to keep an emotional-support dog or similar animal in the unit, both the property’s owner and manager can be sued and even face jail time if the request isn’t granted. Yet, because the ADA makes it illegal to ask about someone’s disability, landlords often give in to the tenant’s demands without having any solid evidence that the pet truly is needed.

In short, you probably will have to allow the tenant to keep her dog – especially if she has a letter from a doctor or other health-care provider that states the animal is needed for her personal well-being.

If it’s any consolation, flight crews at American Airlines have had to make room for everything from miniature horses to emotional-support monkeys in their cabins so their owners wouldn’t have to fly alone, says Tami McLallen, a spokeswoman for the carrier.

Q: I am planning to sell my condominium. I have interviewed three different real estate agents, and all three want to charge a 6 percent sales commission. Aren’t commissions supposed to be negotiable?

A: Yes, federal antitrust laws clearly state that real estate sales commissions are negotiable.

Although most agents charge 6 percent of a home’s selling price as a commission for their services, others will accept 5 percent or even less – especially if their sellers are willing to hold the “open house” events or handle other marketing duties themselves.