As the Senate prepares to take up comprehensive immigration legislation, one of the most pressing questions is how and when illegal immigrants who set out on the path to citizenship qualify for federal benefits.
Lawmakers disagree sharply on this front, which could drive debate as they begin formal work on the bill Thursday.
Sen. Marco Rubio, R-Fla., points out that the proposal says applicants would not qualify for at least 10-13 years -- and would not qualify for another five years after getting a green card, under current law.
Further, Rubio argues that the proposal has "very specific" rules governing anyone who could be considered a "public charge," or someone who would live off the government dole.
"If you are a public charge, you don't even qualify for renewal of that temporary status that you're getting," Rubio said.
But Sen. Jeff Sessions, R-Ala., another Republican senator who has emerged as one of the chief critics of the bill, says the law does not properly enforce that provision.
Sessions told Fox News that the so-called "public charge" law, as currently written, has been "totally ignored" to date. And he argued that many immigrants will be eligible for benefits much sooner than proponents claim -- including the so-called "dreamers," young illegal immigrants brought to the U.S. their parents.
Sessions said 2-3 million illegal immigrants who claim that status will be able to have access to federal benefits in five years.
And, he added, eventually "everyone who entered illegally will be able to accept any benefits this country offers."
After the 15-year waiting period, the number accessing federal benefits could be an additional 10 or 11 million.
Nevertheless, Rubio insists there will be checks at every stage of the process.
"When you re-apply at the six-year mark, by the way you're not eligible for any public benefits at that point, you have to prove you're not a public charge," he said.
A controversial report released earlier this week by the conservative Heritage Foundation estimated that, under the bill, the total cost of legalizing 11 million illegal immigrants could approach $6.3 trillion over the course of their lifetimes. The study factored in taxes those immigrants would pay, but also the services and other benefits that would be spent on them.
It has come under heavy scrutiny from some conservative economists who say it ignored significant factors - like the possibility of some of these illegal immigrants moving up the income ladder after coming out of the shadows, while expanding the economy and boosting federal tax revenue.
Sessions and other critics are unconvinced.
"We respect people who want to come to America. We believe that we should accept immigrants," Sessions said. "But we've got to be realistic about the impact."
As the debate wages on, Sen. Ted Cruz, R-Texas, on Wednesday offered an amendment to end the dispute -- by proposing to let illegal immigrants stay but deny them from ever receiving any "means-tested benefits," or welfare.