With the debate raging over whether immigration reform would gouge taxpayers, Senator Marco Rubio’s office has asked the Social Security Actuary to produce an analysis of the legislation. The findings will provide immigration reform advocates with a major boost.

The most important finding, for the purposes of the debate, is that the Gang of Eight immigration reform proposal would create 3.22 million jobs by 2024, and boost GDP by 1.63 percent. “We estimate a significant increase in both the population and the number of workers paying taxes in the United States as a result of these changes in legal immigration limits,” the analysis says.

But will that population increase mean a huge bill for the taxpayer? When it comes to Social Security, the analysis adds:

we are working to develop full 75-year estimates of the implications of the bill as quickly as possible. Over this longer time frame, benefits will become more significant for those with additional earnings taxed and credited. However, over this same longer time frame, the additional births from the increased population under this bill will have substantial positive effects. Overall, we anticipate that the net effect of this bill on the long range OASDI actuarial balance will be positive.

OASDI is a reference to “Old-Age and Survivors Insurance and Disability Insurance.”

What this means is that in the near term, the cost will grow greater for benefits as formerly undocumented immigrants become legal. That is in line with what critics have alleged in order to derail the legislation. But it also says that this would result in births that would strengthen the balance over the longer run.

The analysis finds that the population of U.S. residents would be boosted by 5.3 million by 2024. That’s also a blow to critics of reform. As Politico puts it:

Critics of the Senate’s immigration bill, such as Sen. Jeff Sessions,  have charged that the figure would be significantly higher and subsequently  burden the U.S. economy by pulling down wages and add more workers to a labor  force already lacking enough jobs.

The SSA analysis cautions that its findings are “preliminary and are subject to change in the future.” But right now, the argument is focused squarely on the claim by conservatives that the costs of reform to taxpayers is prohibitive, regardless (or perhaps irrespective) of whatever economic benefits it provides. This new study will give proponents some powerful pushback.