Tax Day is fast approaching and lots of people are in a frenzy to get their tax returns prepared and filed before the April 17 deadline - including many undocumented immigrants who, contrary to popular belief, pay taxes just like everybody else.

While anti-immigrant proponents would like you to believe otherwise, the Social Security Administration estimates that two-thirds of undocumented immigrants pay payroll taxes.

"When you're working somewhere, your employer's not going to ask you, 'Oh, are you undocumented so I can give you a tax break?'" said Marta, an undocumented 21-year-old clerk who asked that her real name not be used.

Not only do undocumented immigrants pay taxes, they are also helping to fill up the coffers of the Social Security trust fund at a time when the agency is facing a major solvency crisis, even though it is highly unlikely they will ever see any benefit from their contributions.

According to the Social Security Administration, by 2007 its trust fund had received a net benefit of between $120 billion and $240 billion from undocumented immigrants throughout the years, representing between 5.4 percent and 10.7 percent of the fund's total assets that year. So undocumented immigrants are required by law to pay into the system but cannot receive Social Security or Medicare benefits.

"It's unfortunate that people don't see how evident it is that we do pay taxes," said Marta, who came from Chihuahua, Mexico, with her mother on a tourist visa - that they overstayed -when she was only 2 years old.

To many it's anything but evident. How is it possible for an undocumented worker to pay taxes if they are here illegally?

Since they don't have the required papers - namely a social security number and a permanent residency card (or green card) - to begin with, many people believe they must get paid cash under the table.

To be clear, though, according to Stephen C. Goss, the Social Security Administration's chief actuary, about 75 percent of undocumented immigrants are on a company's payroll and therefore have the same kind of withholdings as their documented counterparts.

How do they get on the payroll? There are plenty of ways.

For starters, if they know where to go, they can buy a fake social security number and green card for a couple hundred dollars, which they then use when they're asked for proof of employment eligibility.

Carniceria Guadalajara cashier Tita Saucedo, right, charges Mario and Pam Cruz for purchases, which include sales tax. Immigrants contributed $115 million
Carniceria Guadalajara cashier Tita Saucedo, right, charges Mario and Pam Cruz for purchases, which include sales tax. Immigrants contributed $115 million to Colorado in sales taxes in 2010. (Manuel Martinez/Viva Colorado)

The 1986 law that made it a federal crime to hire anyone who can't provide proof that he's legally entitled to work created a huge black market for these types of fraudulent documents. Most employers are not obligated to check the validity of these work documents, and although many do voluntarily use the government's controversial online checking system known as E-Verify, many simply take these documents at face value - and that's how they end up unknowingly hiring undocumented immigrants.

Some employers, however, do hire them knowingly even though it's illegal. Such is the case with Marta.

"Here at my work, the owner knows my legal status, and he just asked me, 'Just give me anything, any random number so that I can register you,' so I gave him whatever random number came to my head and that's it," the undocumented student explained. "He's just been paying me that way, he hasn't heard anything from the IRS, so he doesn't tell me anything."

Meanwhile, the payroll taxes withheld from Marta's paycheck are going to what the Social Security Administration calls the "Earnings Suspense File," which according to Wendy Sefsaf of the pro-legalization American Immigration Council, "holds the money that's not associated with anyone."

Simply put, the Social Security Administration keeps a record of wages from those whose numbers don't match up with their names. In 2009, the last year for which figures are available, employers reported wages of $72.8 billion for 7.7 million workers who couldn't be matched to legal social security numbers.

The majority of those workers are believed to be undocumented immigrants. The payroll deductions made from those workers' paychecks amounted to $11.2 billion for the Social Security trust fund and $2.6 billion for Medicare. Unless the law changes, most undocumented immigrants will never benefit from that.

"If people are working under a fake social security number, I doubt they're going in and filing tax returns, but they are paying taxes," said Sefsaf. "That's why it's kind of good to at least have the ITIN because when they legalize, they can try to reattach those payments back to themselves so they would benefit from that at some point."

Sefsaf is referring to the Individual Taxpayer Identification Number, which is available to anyone not eligible for a Social Security number - regardless of their immigration status - for the purpose of reporting earnings. "They [the IRS] will take your money," said Sefsaf, even if you're undocumented.

Exactly how many of the ITIN holders are undocumented immigrants is not known, but it's widely believed that it's the majority. According to the IRS, the amount of workers requesting ITINs annually almost tripled between 1999 and 2009, with more than 7.8 million distributed in the past five years.

But why would undocumented immigrants even want to go through the trouble of filing taxes?

"I just do everything in my power to follow the rules, follow the laws," said Marta who uses an ITIN to file taxes every year. "A lot of us just live under such unbearable fear that you try to do everything in your power to do everything right."

And filing a tax return regardless of your immigration status is the right thing to do if you've earned wages, according to retired accountant David Martz, the coordinator for AARP's Tax-Aide site at Centro San Juan Diego, which offers free tax preparation for low-income individuals.

"We don't care [about their immigration status]. They're there to file their taxes, and they're doing the right thing by doing that," the long-time Tax-Aid volunteer said. "I believe no matter if they're here legally or not, they have a responsibility to do their taxes, and I'm going to help them do that."

His wife, Kathy Martz, who is Colorado's communications specialist for AARP's Tax-Aide, said that volunteering at Centro San Juan Diego the past two years has been a humbling experience.

"They're such hard workers, all they want to do is provide for their families," she said. "They're coming in to have their taxes done. If they didn't mean well, why would they be coming?"

Sefsaf believes that undocumented immigrants also file tax returns because if they think they have even the slightest chance of legalizing their immigration status, it will most probably help them "to prove that they've been paying taxes."

In the meantime, pro-immigration advocates like Sefsaf believe that until people accept that undocumented immigrants are not the clandestine population they've been made out to be, myths like the one about how they don't pay taxes will prevail - even in the face of facts that prove otherwise.

People, she said, need to understand that undocumented immigrants - two- thirds of whom have been here for at least 10 years - are "so fundamentally a part of America already that, of course they pay taxes, of course their kids go to school with your kids, of course they own homes, of course they go to PTA meetings, I mean, they're just like everybody else."

Immigrants paid $115 million to Colorado in sales taxes in 2010

While many people are surprised to find out that two of three undocumented immigrants pay payroll taxes, according to the Social Security administration, it should be no surprise that every single one of them also pays sales taxes.

After all, every person in this country is required to pay sales tax whenever they purchase consumer goods, regardless of their immigration status. As one undocumented worker put it, it's not like cashiers are trained to ask people whether they're here legally or not to decide if they should charge them the mandatory tax.

"No person can survive without purchasing things in the United States because we don't have an economy that allows people to be self-sufficient," said Lisa Duran, executive director of Rights for All People. "And we all know that undocumented immigrants shop just like every one else."

In 2010, the Institute for Taxation and Economic Policy estimated that Colorado received nearly $115 million in state and local taxes paid by households headed by undocumented immigrants. And the state was No. 12 on the list, which was topped by California, Texas and Florida.

And these are not the only tax contributions made by undocumented immigrants. They also pay property taxes - historically used as a major source of funding for public education in Colorado - even when they rent. According to ITEP figures, households headed by undocumented immigrants paid almost $22 million in property taxes in 2010, whether directly if they owned a home or indirectly if they rented.

Although there is plenty of information to prove that immigrants pay not only payroll taxes but also sales and property taxes, those spewing anti-immigrant rhetoric have done their job well because this topic continues to be a source of heated debates.

"The bullhorn of folks that are saying undocumented immigrants do pay taxes is unfortunately a lot smaller than the bullhorn of the folks who are repeating the lies," said Duran. "Immigrants - both documented and undocumented - are wonderful, important, vital parts of our society, but not enough of us are trumpeting the fact that we're so much better as a nation for the presence of immigrants in our communities."