After the September 11 attacks in 2001 , the United States again considered placing soldiers along the U.S. – Mexico border as a security measure . In May 2006 , President George W. Bush announced plans to use the National Guard to strengthen enforcement of the US-Mexico Border from illegal immigrants , emphasizing that Guard units " will not be involved in direct law enforcement activities " . Mexican Foreign Secretary Luis Ernesto Derbez said in an interview with a Mexico City radio station , " If we see the National Guard starting to directly participate in detaining people ... we would immediately start filing lawsuits through our consulates . " The American Civil Liberties Union ( ACLU ) called on the President not to deploy troops to deter illegal immigrants , and stated that a " deployment of National Guard troops violates the spirit of the Posse Comitatus Act " . According to the State of the Union address in January 2007 , more than 6,000 National Guard members have been sent to the border to supplement the Border Patrol , costing in excess of $ 750 million
September 11 attacks
September 11 attacks
Illegal immigration to the United States