Editor's note: A version of this story first published in 2019.

(CNN) — It's a surprising fact that's often overlooked in the immigration debate.

Undocumented immigrants pay billions of dollars in federal taxes annually, between tax returns filed and taxes deducted from paychecks, experts estimate.

Here's a look at why — and how — this is happening.

Why some undocumented immigrants choose to pay taxes

The National Immigration Law Center breaks down a number of reasons why undocumented immigrants pay taxes, including:

• It shows they're complying with federal tax laws.

• It can help them demonstrate "good moral character" if they later have an opportunity to legalize their immigration status.

• Tax return records could be used to document work history and presence in the US, steps that may help them be eligible for legal immigration status in the future if lawmakers pass immigration reform.

How some pay taxes despite not having Social Security numbers

Critics of illegal immigration have long argued that undocumented immigrants who pay taxes are able to do so because they're using stolen Social Security numbers. But millions of federal tax dollars are paid every year by people who don't have Social Security numbers at all.

Instead, they file using what's known as an Individual Taxpayer Identification Number (ITIN).

The Bipartisan Policy Center, a Washington-based think tank, notes that "most experts believe the vast majority of tax returns filed with ITINs today are filed by undocumented immigrants."

Some noncitizens who legally immigrated to the United States also pay taxes using this method.

In 2019, according to the IRS, more than 2.5 million tax returns were filed using ITINs, accounting for nearly $6 billion in taxes.

In addition to tax return filings, officials estimate that undocumented immigrants also contribute billions to Social Security annually through payroll tax deductions. In 2010, for example, the Social Security Administration estimated that payments from unauthorized workers accounted for about $12 billion in tax revenue for Social Security.

Immigrant rights advocates are speaking out on social media

In recent years, immigrant rights advocates' posts on Facebook, Twitter, and TikTok during tax season have drawn attention to the issue.

"Undocumented immigrants pay billions in taxes to fund programs they can't access," the National immigration Law Center wrote in a series of recent social media posts.

In 2017, Belén Sisa's post about her experience paying taxes went viral.

"Wanna tell me again how I should be deported, contribute nothing and only leech off this country while the 1% wealthiest people in this country steal from you everyday?" wrote Sisa, who was a college student in Arizona at the time.

The beneficiary of the Deferred Action for Childhood Arrivals program later told CNN she felt it was important to speak out.

"I wanted to show people that we're here, and that we come from all over the world, and that we contribute more than people think that we do," she said.

Jose Antonio Vargas, the Pulitzer Prize-winning journalist-turned-activist who's turned his struggles as an undocumented immigrant into a platform for advocacy, took a break from finalizing his taxes in 2019 to share his experience on Twitter.

"Yes," he wrote, "undocumented immigrants are helping fund the very systems that detain and deport us."

The-CNN-Wire
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