I believe that there is no prohibition on locking your luggage with the small keyed padlocks, but if something in the x-ray process triggers the need for a search of your bags, the lock will just be cut off, and your bags will go the rest of the way unlocked. If your bag doen't need to be searched, the lock will remain intact. The TSA locks supposedly allow the TSA to unlock your bags, search them, and then lock them up again. In my case, the TSA lock disappeared, so I wasn't much better off.