The CBO said the bill would increase gross domestic product by 3.3 percent over the next 10 years compared with current law and by 5.4 percent over the following decade. The agency forecast that 8 million people now here illegally would gain legal status under the bill.
The assessment was not all positive. CBO also said that average wages would decline through 2025 as a result of the bill and that unemployment would go up slightly. And it said that although unauthorized immigrants would find it harder to enter the country and find employment here if the bill became law, some aspects of the legislation would actually increase the illegal population. Some people would overstay visas issued under new temporary worker programs, CBO said, and overall the annual flow of residents here illegally would decrease only by about 25 percent compared with current law.
One critic quickly seized on the impact on pay.
"It's going to raise unemployment and push down wages," said Sen. Jeff Sessions of Alabama, top Republican on the Senate Budget Committee.
Supporters of the bill saw it differently.
Sen. Chuck Schumer, a New York Democrat and a member of the Gang of Eight, said the CBO report "debunks the idea that immigration reform is anything other than a boon to our economy and robs the bill's opponents of one of their last remaining arguments."
The report was issued near the end of a day of skirmishing on the Senate bill, during which senators rejected two amendments delaying legalization until certain security provisions were in place. One would have required additional fencing and the other a new biometric system to track entries into the country and exits.
Those proposals were overshadowed by a larger debate over the legislation's border security requirements, which Republicans generally want to toughen.