Prison Labor Camps

Regular citizens don't have enough motivation to work menial, hard labor jobs for 12 hours a day, 7 days a week! Let's import prisoners to work in the quarries and the factories!
Proposed Pros:
Prisoners need only minimal sustenance (they eat less!) and can work low level jobs with greater efficiency than normal citizens.
Proposed Cons:
Prison needs to be researched.
A prison will need to be built, staffed, and maintained.
Citizens may be unhappy if too many potential jobs are given to prisoners, or if the prison population gets too large.
Prisoners cannot work jobs at more advanced facilities.