From NumbersUSA (italics mine):

The House recently passed H.R. 2638, a Department of Homeland Security appropriations bill. Among the amendments adopted before final passage was a measure sponsored by Rep. Tom Tancredo (R-Colo.), which prohibits homeland security funds from being distributed to states and localities with “sanctuary policies” in place that prohibit or inhibit communications between Federal and state/local authorities.

Although sanctuary policies are illegal under federal law, two states, and numerous cities and counties maintain policies that prevent officials from inquiring about a person’s immigration status or informing federal immigration authorities about the presence of illegal aliens. These policies may stop police from inquiring about a person’s immigration status during the course of routine duties, or from stopping or detaining a person solely due to immigration status.

Campus watchers, take note:

These policies may also prevent state public assistance agencies and institutions of higher education from inquiring about an applicant’s immigration status in order to determine eligibility for public benefits. The resulting safe havens make it easier for illegal aliens, including criminal aliens, to live undetected in the United States.

Sanctuary policies hinder the ability of police to combat increasingly violent criminal alien gangs like MS-13. Such gangs engage in murder as well as the trafficking of drugs and illegal aliens. There are indications that MS-13 may be cooperating with al-Qaeda in smuggling potential terrorists and/or weapons across the border.