Members who are not U.S. citizens should have the "Foreign citizen" or "Foreign corporation" flag checked on their MASTER membership record. This can be done when creating the membership, or by using Tool #15 "Update Membership Information" (shortcut: umbr). Memberships flagged this way will not be included in IRS reporting or tax forms processing.
NOTE: This is different from the "Foreign address" flag, which just controls the format of the member's address. This is so that a foreign citizen can have a U.S. address, or a U.S. citizen can have a foreign address.