The Congressional Research Service released a report to the Senate Judiciary Committee this week that noted a sharp drop in the wages of the bottom 90 percent of tax filers starting in the 1970s, which was when the U.S. experienced a significant increase in the number of immigrants entering the country.
The findings support arguments that Republicans have been making for years now — that bringing in more immigrants will lead to a drop in wages that will hurt U.S. citizens.
And it goes directly against arguments made by the Obama administration, which has said President Barack Obama's plan would do little to affect wages.
According to the CRS report, the percentage of foreign-born people in the U.S. fell between 1945 and 1970, and hit a low of about 5 percent by 1970. During that time, the average income of the bottom 90 percent of tax filers roughly doubled.
Specifically, the number of foreign-born people in the U.S. actually fell, from nearly 11 million to 9.7 million, while wages jumped 82.5 percent.
But from 1970 onwards, the percentage of foreign-born people in the country started rising sharply, and hit about 13 percent by 2013. In that time period, the number of foreign-born people jumped from 9.7 million to 41.3 million people.
At the same time, wages were mostly flat, then rose a little in 2000, then fell to their lowest point in 40 years. In total, they fell 7.9 percent.
The report will likely embolden Republicans to continue to argue against Obama's immigration plan, which could allow up to 5 million illegal immigrants to gain protected status in the United States and work. That plan has been put on hold by a federal court, but the administration is trying to lift the court injunction and allow it to go forward.
Earlier this month, the Social Security Administration admitted it has given out 541,000 Social Security numbers to illegal immigrants under Obama's Deferred Action on Childhood Arrivals plan, which was launched in 2012.