Originally Posted by gooselee

Isn't the case that, technically, TSA cannot restrict you from entering any terminal at an airport so long as you have a valid boarding pass for that airport on that day?

If you look at the threads for the Amex Centurion lounges, there are all kinds of instructions for accessing specific terminals and then having to exit and re-enter security at a different one.

Twice in the past two months I've used the Amex lounge at SFO, then had to switch terminals to get on my DL flight. TSA didn't blink an eye when I showed my DL BP to enter the UA-heavy terminal (in fact, they were so aloof that if I were actually lost, they would have been no help).