It's not that people can do visitation, hold programs, and so on, but Prison Fellowship has a program in which they, in essence, operate part of a prison according to their principles which they've found effective in rehabilitation. Inmates have to agree to participate, they can't just be assigned there.
In at least one state, a program was operating that was very effective in reducing prison violence/crime and recidivism, but it was threatened or shut down because someone in the system objected to its being overtly Christian, with mandatory services, Bible study, and prayer for the participants.
It might have been Texas; I'm vague on details, but I remember reading about it.
I’ve never heard of “Prison Fellowship” sorry. I fail to see how complaints are made of “ with mandatory services, Bible study, and prayer for the participants” if they volunteered to be in the program?