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

Lawmakers called it a step toward a more expansive biometric system that would use identifiers such as fingerprints to keep track of immigrants and visitors exiting the U.S. Currently no such system is in place, something viewed as a security weakness, particularly because some 40 percent of the 11 million immigrants in the country illegally overstayed their visas and there’s no good system for tracking them.

“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, who was absent Monday. “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.

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.

“The entire system, as current law requires, should be implemented,” said Sen. Jeff Sessions, R-Ala., who voted no. “It’s a retreat from current law, a weakening of current law.”

The committee last week rejected an amendment by Sessions to fully implement a biometric screening system. After Sessions’ amendment failed, one of the authors of the immigration bill, Sen. Marco Rubio, R-Fla., announced publicly that he regretted the failure of Sessions’ amendment and would continue pushing for a biometric system to be put in place. The passage of Hatch’s amendment Monday allows authors of the legislation to argue that they’re working to boost security provisions in the bill as Rubio and others have said is necessary to ensure its passage.

The vote happened as the Senate Judiciary Committee plunged Monday into its third week of deliberations on the immigration legislation, which aims to secure the borders, improve workplace enforcement and legal immigration, and offer eventual citizenship to millions of people here illegally. The committee is wading through around 300 amendments as it aims for a final vote on the bill by Wednesday night. Democrats have enough votes on the committee to ensure its passage, which would send it to the Senate floor.

Also Monday the committee approved adding more visas for Tibetans, increasing information sharing among federal agencies when people overstay their visas, and tightening up the nation’s asylum and refugee system so that people would lose their asylum or refugee status if they returned home to the country they fled, unless they can show a good reason for doing so.

Sen. Lindsey Graham, R-S.C., said the asylum change was merited in light of the Boston Marathon bombings. The brothers who allegedly set off the bombs arrived in the U.S. as boys when their family sought asylum here.

An attempt by Sessions to block immigrants who gain legal status under the bill from getting the earned income tax credit was defeated on a party-line vote.

(AP)