Why does the Listing Agreement ask if the Seller is a US Citizen or a resident alien?

The purpose of this question is to determine if the sale will be subject to the Foreign Investment in Real Property Tax Act (FIRPTA). Please click here to read more about FIRPTA and how it might impact a transaction. Both U.S. Citizens and Resident Aliens are exempt from FIRPTA. Please note that Resident Alien is the correct legal term to identify a foreign national living on an official basis in a country of which they are not a citizen.