The Senate will vote Tuesday on four amendments to the comprehensive immigration reform bill, including one that would require a double-layer, 700-mile fence along the southern border before any of the nation’s estimated 11 million illegal immigrants could apply for green cards.

The amendment by John Thune, R-S.D., would require construction of at least 350 miles of the fence before any illegal immigrants would be awarded legal status. The remaining 350 miles would have to be built for legalized immigrants to be able to apply for a green card.

Thune has noted that Secure Fence Act of 2006 called for 700 miles of fencing along the southern border, but only 36 miles has been constructed.

Thune said the fence amendment “would be a tangible demonstration that Congress and this administration are serious about border security.”

Most Democrats oppose the amendment, primarily because they want nothing in the bill that sets a border security condition for legalization or a pathway to citizenship.

Sen. David Vitter, R-La., will offer a related amendment Tuesday that would prevent legalization of any immigrant living here unlawfully until the Homeland Security Department can certify that every entry and exit point in the United States has implemented a biometric visa system.

Democrats and Republicans backing the comprehensive plan are also likely to oppose this amendment because they do not want legalization or a pathway to citizenship to hinge on any border security requirements.

Two other amendments will also be up for a vote. Sen. Mary Landrieu, D-La., has introduced a provision that would make retroactive the Child Citizenship Act of 2000, which provides automatic citizenship for adopted children of U.S. citizens. A fourth amendment, by Jon Tester, D-Mont., would require that Native American tribal officials be included on the Border Oversight Task Force the legislation would create.