On June 11th, the U.S. Senate voted to move the “Border Security, Economic Opportunity, and Immigration Modernization Act” (S. 744), the comprehensive immigration reform bill drafted by the “Gang of Eight,” to the floor for debate, where it is expected to face dozens of amendments in the coming weeks. The final vote to begin debate on the landmark legislation was 84 in favor and 15 against. Below are some of the key issues that this bill faces on its way to a final vote in the Senate:

Border Security: Senator John Cornyn (R-TX) has signaled support for implementing border security triggers – including a 90% apprehension rate of illegal border crossings – before putting undocumented immigrants on the path to permanent residency. Senator Cornyn’s amendment would also introduce a biometric exit system as well as a nationwide electronic employment eligibility verification program. The measure has already stirred opposition from Democratic senators and immigration advocates, who liken it to a “poison pill” that will indefinitely delay the citizenship prospects of the estimated 11 million undocumented immigrants already in the United States.

Senator Marco Rubio (R-FL), a member of the “Gang of Eight,” has also indicated that he may not be able to support the legislation in its current form without strengthened border security measures. To this end, Senator Rubio and his colleague, Senator Tom Coburn (R-OH) may propose an amendment that would transfer the responsibility for drafting, but not enforcing, a border security plan from the U.S. Department of Homeland Security (DHS) to Congress. Several other drafters of the bill, including Senator Charles Schumer (D-NY), expressed a willingness to include border security triggers so long as they are “both achievable and specific.”

Taking a more expansive approach, Senator Rand Paul (R-KY) plans to offer an amendment that would require Congress to draft and enforce a border security plan, as well as to vote on border security every year for the first five years after the bill takes effect. Democratic senators and immigration advocates oppose this measure, citing unpredictability and partisanship as future hurdles to implementing a path to citizenship.

Taxes: Senator Jeff Sessions (R-AL) plans to re-introduce two amendments that would require families to provide a valid Social Security number to receive a child tax credit and deny the earned-income tax credit to immigrants with temporary legal status, respectively. Both measures previously failed in committee on a party-line vote.

Senator Orrin Hatch (R-UT) is also expected to offer an amendment that would require immigrants to demonstrate that they have paid back taxes and remained current on present obligations as they progress toward citizenship. Senator Hatch may also introduce a measure that would ban immigrants who are legal permanent residents from receiving Affordable Care Act subsidies for five years.

Guns: Senator Richard Blumenthal (D-CT) may offer two amendments restricting access to guns for undocumented immigrants. One of the provisions would eliminate the loophole that allows certain immigrants to purchase firearms, while another would require the Attorney General to alert the Secretary of Homeland Security when an undocumented immigrant or temporary visitor to the U.S. attempts to buy a firearm. Currently, both categories of individuals are legally barred from purchasing firearms.

Same-Sex Benefits: Senator Patrick Leahy (D-VT) is weighing whether to revive an amendment that he reluctantly declined to introduce in committee due to the opposition of his Republican colleagues. The measure would permit U.S. citizens in state-recognized same-sex marriages to apply for permanent residency on behalf of a same-sex spouse, a benefit that is currently afforded to heterosexual couples only.