ABA rules. No working more than 20 hrs/week.
A student may not be employed more than 20 hours per week in any week in which the student is enrolled in more than twelve class hours.
I haven't found anything on the ABA website saying that it enforces it. I think it's more a regulation so that the univeristy can't offer you a 30 hour/week work study program or encourage you to work more for any reason. However if you want to go take on a 30 hour PT job on your own...I guess it's on you, but then you can't complain about it if finals rolls around and you're unprepared.
I am going into my second year soon, and we DO have to sign something every semester that says we are not working more than 20 hours a week. The ABA requires the school to do this. I would not want to work more and have signed something that I lied on.