My issue is simple:
Nobody has the right to stop me and prevent me from moving in the public area of an airport based on the rules of an air carrier which only apply once I arrive at a private gate or aircraft.
The airport my 'authorize' these people; the airline may wish to have bags stopped before they reach the gate, but the question is 'do they have the legal right?'
I do not believe this matter has been settled nor addressed.
This is not an issue of 'can I take on oversized bags'....the question is "can you stop my free access to public space for ANY reason?' Must I show someone other than a TSA agent my 'documents' prior to entering a TSA controlled area?
(just because an airport authorizes a third party 'security' firm to ask to see your documents does not mean this is a legal requirement. In fact it may be entirely based on a legal opinion that says 'we can ask for voluntary compliance, but we have no legal authority" to which all involved say "OK, we can live with that- lets go forward with this program")
I agree you should not take oversized bags onto the plane. I agree the airline has a business reason to prevent this. All true. Neither of these things give anyone the right to stop and question you prior to arrival at a private airline space.
If anyone can cite legal references, that would be interesting
Golfingboys advice is fine if you have 30 minutes to hours to wait for an AA station manager to show up.... I once went back and forth twice between security and AA ticket counter- finally I demanded the agent walk with me, I suspect the only reason they did so is that I was CK at the time.