Source?

Why are to so adamant that it is a TSA policy? It's not. Policy is policy and I think we all know how much the TSA likes enforcing their policies. If this was TSA policy airlines would be getting fined left and right for non-compliance. As I said earlier, I was a supervisor at an airport for two airlines before I became a pilot. Trust me, TSA policy is drilled into your head on a daily basis because of the fear of fines, etc. I can speak from quite a bit of experience when I say that I am almost 100% certain this is not a TSA requirement as one of the airlines had it published right in their training material that a passport was not required, while the other airline did require a passport.

I'm honestly not trying to be argumentative. I'm just curious why you seem so sure of your answer when I have quite a great deal of experience in this area and know it to be wrong.