Authority of State and Local Police to Enforce Federal Immigration Law
"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.

Congressional authority to prescribe rules on immigration does not necessarily imply exclusive
authority to enforce those rules. In certain circumstances, Congress has expressly authorized
states and localities to assist in enforcing federal immigration law. Moreover, there is a notion that has been articulated in some federal courts and by the executive branch that states may possess “inherent” authority to assist in the enforcement of federal immigration law, even in the absence of clear authorization by federal statute. Nonetheless, states may be precluded from taking actions that are otherwise within their authority if federal law would thereby be thwarted..."