US President Barack Obama has signed into law a $US600 million bill providing increased security along the US-Mexico border.
The Senate reconvened on Thursday during its August recess to pass the measure.
The funds will mostly be directed to activities on the south-west border, such as hiring 1000 border patrol agents.
Money will also pay for surveillance technology, including unmanned drones.
A further 250 immigration and customs enforcement agents will also be funded by the bill.
However, Homeland Security Secretary Janet Napolitano said it would take eight months for the new border patrol agents to be recruited, trained and deployed to the border.
She also said that border crossings into the United States were down 50% as a result of extra security and a weakened economy with fewer jobs for migrants.
The $US600 million will be funded by raising fees on some foreign work visas.
The BBC reports Thursday's session was only the second time in four decades that the Senate has been called back into session during August.
The other time was to pass emergency measures related to Hurricane Katrina in 2005.
