I manage rental properties for a client who doesn’t want people smoking on his property. If we deny potential tenants’ applications because they smoke, will this violate any federal fair-housing laws?

No. Federal fair-housing laws make it illegal for the landlord to choose tenants based on their race, color, sex, national origin, religion, handicap, and familial status. However, people who smoke are not a protected class. A landlord can refuse to lease to potential tenants who smoke as long as the landlord consistently enforces such prohibition.