A document published by the Internal Revenue Service that details tax requirements for workers earning an income in the United States who are non-resident aliens. Income earned in the United States is taxed regardless of citizenship status, although non-residents who do not earn income, such as tourists, or who do not conduct business do not have to file a return. If a worker in the United States earns income from abroad or has income exempt from U.S. taxes, that worker still has to file a return. Wages, rents, interest, dividends and income from business activities are subject to taxation.

Workers in the United States are considered non-resident aliens if they do not have a green card (not a lawful permanent resident) or if they do not pass the substantial presence test. However, non-resident aliens can seek to be treated as residents for a part of the year, meaning that someone can be both a non-resident alien and a resident during the same tax year. More information on this can be found in IRS Publication 519 (U.S. Tax Guide for Aliens).