I wonder how long I'd have my house if I'd tell the mortgage company "I'm the only one who gets to interpret my loan contract and from the way I read it I only have to pay you half of what it says each month."
No one flying an airplane or at the AOA would ever try to exceed the FTLs or use them as an excuse to extend and/or do something illegal or unsafe; it's more of a 'no go' safety valve. Made by someone when a duty would be questionable in either legality or safety. So a lot of this is simply rhetoric but the premise is inconceivable. Piddly little stuff.
In any case, would it actually become an issue the whole thing would be adjudicated by a judge or jury anyway--who wouldn't be particularly moved by self-proclaimed authoritarians. With plenty of other folks providing their viewpoint as well (interestingly enough employing US nationals/residents and the L-1 visa trail could likely give them standing in a US arena as well would this come to pass). The letter IMHO is simply an attempt at intimidation for folks not easily intimidated.
Their rhetoric department could really use better writers.