Renting to rehab agency

[Mal K.]

I was contacted by a representative from a rehab agency for recovering,non-violent, drug/alcohol abusers. I don't feel comfortable with the situation, new tenants every 6 months, 4 adults sharing the apartment, etc. I put on the ad for the apartment I was willing to accept tenants with non-violent records. 

Questions:

Do I have to provide an application even though I won't be renting to them?

Is there any discrimination laws that pertain to this situation?

What should I write in the reply to the representative I spoke with?