I had checked our state law and unfortunately found this one to be true; I don't just take someone's word for it. Our rookie year when I started the team and got ready to place a big AndyMark order on my credit card, I got nailed with the you-can't-order-stuff-without-an-approved-PO speech and was told that was state law. At week 3 of build season and still no PO's approved, I checked and it wasn't the case - the school board was very sympathetic to understanding our needs during build season and waived their "local policy" for us.
Here is a copy of the current policy on vans in Alabama