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KAI RYSSDAL: The Senate today voted for a 370-mile fence along the Mexican border. It also voted in favor of giving millions of illegal immigrants a legal path to citizenship, despite objections in the House. Crossing the border illegally is supposed to be tough. Emotionally and practically. People trek through the desert, or swim the Rio Grande . . . at night. For years, would-be immigrants have used smugglers to get them across. Stuffed in the back of a truck. But Sanden Totten reports the business of illegal immigration is getting a lot more sophisticated.

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SANDEN TOTTEN: This shopping center in South Minneapolis attracts some people with its low prices. Others come to its parking lot to buy false green cards, passports and Social Security numbers. Dealers keep the documents hidden in their trunks. There could be dozens in the back of any one of these cars.

Six years ago, a woman we'll call Erica was also hidden in the trunk of a car. She was five months pregnant and it was the last leg of a long journey. Erica is a single mother from Mexico.

ERICA [translation]: "I didn't see a future in Mexico because in my culture, single moms are looked down upon. I wouldn't have been able to support my son financially either."

Erica now lives in Minnesota with her son. The first two times she tried to cross into the US she went by foot. She was led by hired guides known as "coyotes". Both times she was caught and sent back to Mexico. Then she found the professionals.

These coyotes ran their operation out of a large house in Tijuana. They didn't come cheap, but she noticed the difference right away.

ERICA [translation]:"They had separate rooms for men and women. They had extra clothes. They had desks, they had secretaries who falsify documents of all kinds."

When she entered the ID factory she was another poor, small-town girl looking to get out. But when she left, she was a wealthy Mexican government official. She had the look, the clothes, even the legal documents to prove it.

Instead of the usual coyote leading her through the desert, this one was dressed as a cab driver. He was supposedly driving Erica around on a shopping trip in the US. During the crossing, she remembers getting very nervous, but the coyote even had a pill to keep her calm.

ERICA [translation]: "I'm not sure what kind of pill that was but I felt great. He controlled us and helped us cross. If you're crossing the border by car, coyotes always warn that there are cameras everywhere. So he'd tell us to start laughing now or start talking about shopping, not to get nervous, he'd reassure us nothing bad was going to happen. He was intelligent. He wasn't like other coyotes."

Once in the US, Erica rode with a series of drivers who helped move her through Southern California. On the last leg of her journey though, she and two others were crammed into the trunk of a car as a precautionary measure. She eventually arrived safely in Los Angeles.

This kind of operation isn't unusual, says Mark Cangemi of the Upper Midwestern bureau of US Immigration and Customs Enforcement. He says in recent years there have been reports of professional networks like these growing and even competing against each other.

MARK CANGEMI: "Its organized crime! There are family groups on the border whose whole livelihood is based on smuggling. It could be smuggling people, it could be smuggling narcotics or it could be both."

Cangemi says because of tighter border security, smuggling organizations have had to adapt to survive. The result is that these networks have become far more sophisticated, sometimes with operations in several different countries. And they spread deep into the U.S. as well.

People like Erica can't fully escape these networks, even here in Minnesota. Soon Erica's fake green card will "expire".

She'll have to come to a spot like this parking lot to buy a new one. She leads a normal life here in the US. She has a job, pays taxes and her son is in school. She hates dealing with the ID merchants. She says it makes her feel like a criminal. But to keep the life she's built for her son and herself, she says she has no other choice.

ERICA [translation]: "When time goes by, you realize that an illegal document is just that, and what matters is what you make of your life because there's a lot of illegal people and the illegal person who does real crime pays for it. But if you're good, then life should be good, no matter where you are."

In Minneapolis, I'm Sanden Totten for Marketplace.