Foreigners leaving the country through any of the nation's 30 busiest airports would undergo mandatory fingerprinting under an amendment senators added to an immigration bill.

Currently no such system is in place, and some 40 percent of the 11 million immigrants in the country illegally overstayed their visas and there's no good system for tracking them, said AP.

"This is an agreement that we need to build toward a biometric visa exit system," said Sen. Jeff Flake, R-Ariz., who offered the amendment by Sen. Orrin Hatch, R-Utah. "Implementing this biometric exit system is long overdue."

A full-fledged biometric entry-exit system is favored by many senators but was deemed too expensive and unworkable to include in the bill. Current law already requires such a system to be in place, but the Department of Homeland Security has not implemented it. Instead the bill seeks electronic scanning of photo IDs, said AP.

Under Hatch's amendment, the nation's 10 busiest airports would have to establish a fingerprinting system within two years after enactment of the immigration bill. Within six years it would have to be in place at the 30 busiest airports.

The amendment passed 13 to 5.