Company has an operation in the US employing US nationals on US soil. While absent a collective unit in the US some industrial matters might not be easily addressed there, statutory matters most certainly do fall under the jurisdiction of the US. There are some exemptions for foreign carriers, but what one law giveth another taketh away. It is hard to reverse position on something you say applies one minute and not the next. Especially if you also have some intrastate operations and duty occurring (I.e the company operation is mostly international with respect to its flights and duties but not exclusively so).
I would have just let it ride were I them and not rocked the boat.