As I understand it, TSA handles the actual security screening, but the folks that match IDs to Boarding Passes and tell you what line to go to are Airline employees.

So what happens if you go to the short elite line, when the ID checker has told you to go to the long commoner line? Ultimately, would the aiport police show up and support the ID checker by arresting you if you refuse to go to the proper line? Or would the TSA folks get involved? Or, is the elite security line more of a common courtesty thing and if one of the "unwashed" wants to be an ... and use it, they *legally* can?