State and Local 'Sanctuary' Policies Limiting Participation in Immigration Enforcement [March 23, 2017] [open pdf - 651KB]
"The federal government is vested with the exclusive power to create rules governing which aliens may enter the United States and which aliens may be removed. However, the impact of alien migration-whether lawful or unlawful-is arguably felt most directly in the communities where aliens reside. State and local responses to unlawfully present aliens within their jurisdictions have varied considerably, particularly as to the role that state and local police should play in enforcing federal immigration law. While some states and municipalities actively participate in or cooperate with federal immigration enforcement efforts, others have actively opposed federal immigration authorities' efforts to identify and remove certain unlawfully present aliens within their jurisdictions. [...] This report provides examples of various state and local laws and policies that fall into one of these sanctuary categories. The report also discusses federal measures designed to counteract sanctuary policies. [...] Additionally, the report discusses legal issues relevant to sanctuary policies. In particular, the report examines the extent to which states, as sovereign entities, may decline to assist in federal immigration enforcement and the degree to which the federal government can stop state measures that undermine federal objectives in a manner that is consistent with the Supremacy Clause and the Tenth Amendment."
CRS Report for Congress, R44795
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html