Fair Housing: Feds on Service Animals and Assistance Animals.
http://portal.hud.gov/hudportal/documents/huddoc?id=servanimals_ntcfheo2013-01.pdf
Bottomline: Make reasonable accommodations for disabled tenants (physical/mental issue that affects at least one major life function) and their service animals (dogs) and assistance animals (other animals providing services and emotional support) without charging extra money such as pet deposits.