This is a true stab in the dark here, but I suspect this has nothing to do with US regulatory requirements (there are none of which I am aware) and everything to do with capacity controls imposed on AF/KL as a result of their joint venture with Delta. Without getting into boring specifics, they are supposed to run at rough parity in terms of the number of seats between the US and Europe. AF/KL have had more than half the seats for several years and that has been a bone of contention among Delta pilots who view the imbalance as an outsourcing of flying they should be doing, which is an issue in upcoming 2015 contract negotiations, further complicated by the Delta/Virgin JV.