Sen. Jeff Sessions (R-Ala.), an outspoken critic of the Senate immigration reform bill, predicted Sunday that GOP opposition to the measure will grow as lawmakers learn more of its details.

The bill’s sponsors unveiled a nearly-1,200 page amendment to the legislation Friday that would double the number of patrol agents and authorize the construction of 700 miles of fencing along the U.S.-Mexico border.

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Sessions said few lawmakers will have a chance to read and understand the amendment before voting on it Monday. If they do, he predicted, GOP support for the compromise amendment drafted by Sens. Bob Corker (R-Tenn.) and John Hoeven (R-N.D.) will dissipate.

“They said it had 70 votes last week and then all of a sudden it started sinking when people learned more about it. I think if people find out this amendment does not accomplish what the sponsors believe it does, I think the bill could be back in trouble again,” he said on CBS’s “Face the Nation.”

Sessions noted that the deployment of 20,000 additional border patrol agents is not required until 2021 and does not appropriate funds but only authorizes them. He added the legislation includes a provision that empowers Homeland Security Secretary Janet Napolitano not to construct the border fence if she believes it’s unwarranted.

“She’s publicly said that we’ve had enough fencing,” he said.

“The reason this bill was in trouble, the reason this amendment was thrown in here at the last minute was because the promises weren’t fulfilled and this legislation, this amendment doesn’t fulfill its promises, either,” he added. “We’re going to have amnesty first, no enforcement in the future, we’re going to have continued illegality.”

Corker, appearing on the same program, predicted the bill would pass with a large bipartisan majority. He said Republican senators who are on the fence should consider a report from the Congressional Budget Office projecting large deficit reductions.

“To be able to pass a bill that spends $46 billion on border security over a ten-year period but know that you’re going to have a return of $197 billion without raising anybody’s taxes, that will reduce our deficit, ought to also entice people to this bill,” he said.

Sessions and other critics, however, have argued that the CBO analysis is inaccurate because it only counts taxes that legalized immigrants will be paying into Social Security and Medicare without counting the drain they will put on those programs decades in the future.