I have a client that who is an Amazon seller and who resides in a country that has a tax treaty with the U.S. They are taking the position that their business profits are tax exempt because they do not have a permanent establishment in the U.S. (I'm not asking for advice on the merits of this position)

Since they have done so, do I need to file a schedule C on a 1040NR and also claim the treaty position? Or do I simply not need to file anything for them because all of their U.S. income is tax exempt?