Maria Isabel de la Paz is a 30-year-old Houstonian who works at a Chick-fil-A. She holds the distinction of being a U.S. citizen who was prevented for a dozen years from entering the United States.

Her case is at the heart of what immigrant advocates say is wrong with U.S. immigration enforcement — that deportations are increasingly being handled by federal agents at the border, rather than in immigration court. The practice is not necessarily illegal, but critics say it is fundamentally unfair.

De la Paz was born in the U.S. But when she was 4 months old, she says, her parents — who were both in Texas illegally — took her back to their home in Michoacan, Mexico. And that's where she grew up.

Twice, de la Paz tried lawfully to enter the U.S. port of entry at Brownsville, Texas, with her Texas birth certificate in hand. Both times, agents said the document was falseand sent her back. So earlier this year, she decided to cross the river illegally to join her mother, who was again living in Houston. She got caught.

"When the agent questioned me, I said I was born in Houston," de la Paz says. "He smiled. He asked, 'Why are you crossing this way?' I said, 'It's because you won't accept my birth certificate.'

"He asked, 'If you're a citizen, why can't you speak English?' I said my parents took me to Mexico when I was an infant, and I've been trying to return ever since. Then, he just laughed at me."

De la Paz's mother hired an immigration attorney, who was able to convince the U.S. Embassy in Mexico City that Maria was, indeed, an American by birth. She finally got her U.S. passport last summer.

De la Paz's lawyer,Jaime Diez, says Maria should have been given a chance to make her case to an immigration judge, but she wasn't. And her case is not all that uncommon on the border, Diez says.

"Unfortunately it is not. Cases like hers are more common every day," he says. "We have given a lot of power to agents at ports of entry, CBP [Customs and Border Protection]. There's something wrong with an officer being able to take away someone's citizenship, throw them into Mexico and close the case."

Diez represents more than 50 clients who are U.S. citizens who were born via midwives in Texas and cannot obtain passports. Some have been refused re-entry. Immigration agents are suspicious of birth certificates issued by midwives because of fraud in the past.

This month, the American Civil Liberties Union released a lengthy report focused on these summary deportations. The ACLU calculates that 83 percent of all removals last year were handled by immigration enforcement officers, without formal review. Most of them took place at the border.

Sarah Mehta, a human rights researcher at the ACLU and author of the report, says she thinks "there's a problem with the assumption that just because you're at the border, you're in an area where people don't have rights."

In its defense, the Department of Homeland Security wrote in an email, "Individuals in DHS custody maintain important rights and due process protections throughout the course of their proceedings. An individual may be removed from the U.S. only after any claims for relief from removal, including asylum, are fully evaluated."

Immigrant advocates counter that noncitizens' claims to enter this country can only be fully evaluated by an immigration court employee, not a uniformed agent.

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