[Excerpt] The Immigration and Nationality Act (INA) provides that all aliens (i.e., persons who are not citizens or nationals of the United States) must enter pursuant to the INA. The major categories of aliens are immigrants, refugees and asylees (all admitted for or adjusted to legal permanent residence), and nonimmigrants (admitted for temporary reasons, e.g., students, tourists, or business travelers). Foreign nationals who lack proper immigration authorization are generally of three kinds: (1) those who overstay their nonimmigrant visas, (2) those who enter the country surreptitiously without inspection, and (3) those who are admitted on the basis of fraudulent documents. In all three instances, the aliens are in violation of the Immigration and Nationality Act (INA) and subject to removal. As a signatory to the United Nations Protocol Relating to the Status of Refugees (hereinafter, U.N. Protocol), the United States agrees to the principle of nonrefoulement, which means that it will not return an alien to a country where his life or freedom would be threatened. Nonrefoulement is embodied in several provisions of U.S. immigration law. Most notably, it is reflected in the provisions requiring the government to withhold the removal of aliens to a country in which the alien’s life or freedom would be threatened on the basis of race, religion, nationality, membership in a particular social group, or political opinion.