"A refugee is a person fleeing his or her country because of persecution or a well-founded fear of persecution on account of race, religion, nationality, membership in a particular social group, or political opinion. Typically, the annual number of refugees that can be admitted into the United States, known as the refugee ceiling, and the allocation of these numbers by region are set by the President after consultation with Congress at the start of each fiscal year. [...] Special legislative provisions make it easier for members of certain groups to obtain refugee status. The 'Lautenberg Amendment,' which was first enacted in 1989, allows certain former Soviet and Indochinese nationals to qualify for refugee status based on their membership in a protected category with a credible fear of persecution. In 2004, Congress amended the Lautenberg Amendment to add the 'Specter Amendment,' which requires the designation of categories of Iranian religious minorities whose cases are to be adjudicated under the Lautenberg Amendment's reduced evidentiary standard. The Lautenberg Amendment, as amended by the Specter Amendment, has been regularly extended."
via Federation of American Scientists: http://www.fas.org/sgp/crs/index.html