Anchor babies born in U.S. jumped 48% in 2009, a fact certain to fuel controversy over proposals to halt birthright citizenship

The total number of children in the USA born to illegal immigrants on U.S. soil jumped to 4 million in 2009, up from 2.7 million in 2003, a report released Wednesday estimates.

Those children — who are automatically granted U.S. citizenship — represent 5.4% of all children under the age of 18 in the U.S. That compares to 3.7% six years earlier, according to data from the non-partisan Pew Hispanic Center. That percentage will continue rising, as an estimated 340,000 of the 4.3 million babies born in the U.S. in 2008 alone — about 8% — came from illegal immigrant parents, the report says.

The study comes as some legislators, including Sen. Lindsey Graham, R-S.C., are calling for a revision of the 14th Amendment that grants citizenship to anyone born in the United States.

The percentage of native-born people in the U.S. has fallen for four straight decades, according to the U.S. Census Bureau. In 2008, 12.5% of the population was born outside the U.S., nearing the all-time highs of nearly 15% in the late 1800s.

"The share of the population that is white non-Hispanic is going to drop," said Jeffrey Passel, senior demographer of the Pew Hispanic Center. "The percentage that consists of immigrants and their children is going to increase."

Bob Dane, a spokesman for the Federation for American Immigration Reform, which wants lower levels of legal and illegal immigration, said automatic citizenship for children born in the U.S. is one of the main magnets for illegal immigration.

Dane said many illegal immigrants are searching for jobs. He said many others come here to have a baby who is entitled to a wide array of government benefits and can eventually help the parents become citizens as well. He calls the practice a "corruption of the rule of law."