Authority of State and Local Police to Enforce Federal Immigration Law [September 17, 2010] [open pdf - 260KB]
"The power to prescribe rules as to which aliens may enter the United States and which aliens may be removed resides solely with the federal government, and in particular with Congress. Concomitant to its exclusive power to establish rules which determine which aliens may enter and which may stay in the country, the federal government also has the power to sanction activities that subvert this system. Congress has defined our nation's immigration laws in the Immigration and Nationality Act (INA), a comprehensive set of rules for legal immigration, naturalization, work authorization, and the entry and removal of aliens. These requirements are bolstered by an enforcement regime containing both civil and criminal provisions. Deportation and associated administrative processes related to the removal of aliens are civil in nature, while certain violations of federal immigration law, such as smuggling unauthorized aliens into the country, carry criminal penalties."
CRS Report for Congress, R41423