Senator Jeff Sessions, R-Ala., references letters from officials at ICE and the Customs and Immigration Enforcement Association while criticizing proposed U.S. border security under the Gang of Eight's immigration plan.

Aiming to advance a sweeping immigration reform bill by week’s end, senators on the committee considering the legislation planned marathon sessions to complete its edits, including the approval Monday of a compromise measure to implement a test system for taking foreign visa holders’ fingerprints when they exit the United States.

In an effort to win over Republicans who favor using “biometric” criteria – like fingerprinting -- to monitor when foreigners leave the country, pro-reform members of the Senate Judiciary Committee approved an amendment sponsored by Sen. Orrin Hatch of Utah, a Republican considered to be a swing vote on the 18 member committee. That amendment, a less stringent version of a biometric proposal that failed last week, would require the Department of Homeland Security to establish a fingerprinting system at the 10 U.S. airports with the highest international traffic within two years. After six years, that system would have to be in place at the nation’s 30 biggest airports.

Chip Somodevilla / Getty Images Senate Judiciary Committee holds a markup session on the immigration reform legislation in the Hart Senate Office Building on Capitol Hill May 20, 2013 in Washington, DC.

The biometric tracking is primarily aimed at monitoring visa overstays, which account for an estimated 40 percent of the undocumented population.

It was adopted by a vote of 13-5.

Florida Sen. Marco Rubio, a Republican who is not on the Senate Judiciary Committee but was a key drafter of the Gang of Eight legislation, has been pushing for the biometric system.

In a statement, Rubio applauded the passage of the Hatch amendment.

"The amendment adopted today is a good start and I will continue to fight to make the tracking of entries and exits include biometrics in the most effective system we can build when the bill is amended on the Senate floor," he said.

Prior to the vote, Sen. Jeff Sessions of Alabama – who sponsored an attempt last week to immediately begin implementation of a fingerprinting system at all major air, sea and land ports – slammed the amendment as inadequate, disputing the idea that finalizing a nationwide system would be costly and unwieldy.

“Why we won’t do it and do it properly within a year or 18 months – completely -- I have no idea,” Sessions said.

Congress has previously passed legislation requiring a biometric exit system but has never implemented the program, citing cost, infrastructure challenges and opposition from major airlines.

Proponents of the Hatch measure said it would provide an important step towards implementing a more complete biometric system, which senators on both sides of the aisle agreed would provide the most failsafe method for tracking visa overstays as well as individuals who pose national security threats.

“I do not look at this, Senator Sessions, as a fig leaf,” said Democrat Sen. Dianne Feinstein of California. “I look at it as a start.”

Republican Sen. Jeff Flake of Arizona, another Gang of Eight member, added that all lawmakers are “frustrated” by the fact that a biometric system has not yet been implemented nationwide but that the Hatch measure would be the most “aggressive” mandate yet to start putting one in place.

Senators Jeff Sessions, R-Ala., and Chuck Schumer, D-N.Y., discuss the use of biometric screening at the nation's airports at a Senate immigration hearing on Monday.

Earlier Monday, senators also approved an amendment proposed by South Carolina Sen. Lindsey Graham, also a member of the Gang of Eight, that would void legal status for individuals who sought asylum in the United States but subsequently returned to the country from which they fled.

That measure was aimed at those like Boston Marathon suspect Tamerlan Tsarnaev, whose family had been granted asylum in the United States but who had returned to Russia prior to the terrorist attack.

Senators also unanimously approved an amendment to mandate better tracking of immigrants who have overstayed visas by mandating broad data-sharing between customs officials, federal law enforcement and intelligence personnel.

The committee was slated for a late night Monday. As it began its fourth day of edits to the bill, Chairman Sen. Patrick Leahy said he was optimistic that the panel could complete its work as early as Wednesday night.

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