WASHINGTON (AP) — Millions of immigrants benefiting from President Barack Obama's executive actions could get a windfall from the IRS, a reversal of fortune after years of paying taxes to help fund government programs they were banned from receiving.

Armed with new Social Security numbers, many of these immigrants who were living in the U.S. illegally will now be able to claim up to four years' worth of tax credits designed to benefit the working poor. For big families, that's a maximum of nearly $24,000, as long as they can document their earnings during those years.

Some Republicans are labeling the payments "amnesty bonuses," one more reason they oppose Obama's program shielding millions of immigrants from deportation.

"I represent hard working, law-biding Texans," said Rep. Sam Johnson, a senior Republican on the House Ways and Means Committee. "I think these amnesty rewards, and that's what they are, need to be stopped."

Advocates argue that many of these immigrants pay taxes, so they should be able to claim the same tax credits as anybody else. Over the past decade, immigrants in the U.S. illegally have paid an estimated $100 billion in Social Security payroll taxes, even though few will ever be able to collect benefits, said Stephen Goss, Social Security's chief actuary.

Obama has issued executive orders shielding about 4 million immigrants from deportation. Some were brought to the U.S. as children; others are parents of children who are either U.S. citizens or legal residents.

Republicans in Congress oppose Obama's actions and are trying to use a funding bill for the Department of Homeland Security to overturn them. Democrats are resisting, resulting in a stalemate that is threatening to shut down the department.

Funding for the department, which oversees immigration enforcement, runs out Feb. 27.

The dispute over tax credits illustrates the complicated relationship that many immigrants have with the U.S. tax system. Social Security estimates that immigrants living in the country illegally work at about the same rate as the rest of the population, even though federal law bars them from employment.

In general, they are less likely to pay federal taxes. Those who do have been boosting Social Security's finances for years.

There are an estimated 11 million to 12 million immigrants in the U.S. illegally. At least half are paying income and payroll taxes, even though few have valid Social Security numbers, according to the nonpartisan Congressional Budget Office.

By law, you must have a Social Security number to work in the U.S. But millions of people work without them.

Some work in the underground economy and do not report their income to the government. For those who work and pay taxes, the IRS provides them with an Individual Taxpayer Identification Number (ITIN).

Since 1996, the IRS has issued 21 million of these numbers. About one-quarter of them are still in use, the agency says.

The IRS accepts these tax returns without reporting the taxpayers to immigration authorities, IRS Commissioner John Koskinen said. That encourages the workers to pay taxes.

"We don't enforce the Social Security laws, we don't enforce the immigration laws," Koskinen said of his agency. "In fact, the reason illegal immigrants file taxes with us is they know we aren't sharing that data with anybody. We treat it as taxpayer-protected information."

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