Hundreds of National Guard troops will begin arriving along the southwest border in two weeks.
The 1,200 guardsmen, assigned to help protect the border, are to be fully deployed by September.
Federal officials say the U.S. side of the border is more secure than ever, and that troops on the ground will add to that security.
As to rules for engagement?
"The National Guard will be there to support the efforts of law enforcement, not to confront unless confronted any particular threat," explained U.S. Customs and Border Protection Commissioner Alan Bersin.
Stationed in Arizona, California, New Mexico and Texas, Guard troops will help the border patrol watch for smugglers and illegal border crossings.
They'll also aid in intelligence gathering.
Meanwhile, Arizona's law that makes it a state crime to be in the country illegally is scheduled to take effect July 29th.
It allows an officer to question a person about their legal status when there's suspicion that person is in the country illegally.
The Obama administration argues that border control is a federal responsibility and should not be left to each state.