The Sunport driver told me it was FAA, but I didnt believe him. He said that if a passenger had something on his clothing, such as, oh, I don't know, anthrax, or some disease or biological agent, it might accidently brush against the pilot or FA, and then they might carry it across the country on their next flight. I asked him why I was able to be around them in a plane or in the airport. He said, "I guess it only matters on a shuttle bus".
Sounds pretty far-fetched, but that is how it went.