the first thing you have to do is to standerdize one USB key and based your policy on that. if you just disable USB you will have probleme with laptops using mouce and KB. also PCs will have probleme.
so you have to define what you want to block
do you want to track what is transfer to usb
do you want to encrypt your usb
you need to know why you want to restrict acces to USB some time the cost of implementing this kind of policies cost much more than what you can save.