Over the past decade, towns and counties across the United States have been locking up a growing number of people for failing to pay their debts. The American Civil Liberties Union and the Brennan Center for Justice documented the practice in 2010, and Human Rights Watch released the results of its own investigation earlier this year.

Critics have decried the return of the debtors prison, the reviled institution of Charles Dickens' day. Now, a short documentary, "To Prison for Poverty," sheds light on a particularly contentious aspect of the story.

In Alabama, Georgia, and other Southern states, many local governments have signed contracts with "private probation" companies -- for-profit firms that specialize in collecting fees and fines from people who owe the courts money for low-level infractions, usually traffic-related. Halli Wood, an unemployed 17-year-old from the small town of Columbiana, Alabama, told Brave New Films she was placed on probation with one of the largest of these companies, Judicial Correction Services, or JCS, after she couldn't come up with the money to pay off a seat belt ticket.

Although Wood couldn't afford the $41 ticket, the company charged her an additional 45 dollars in fees. Like other private probation companies, JCS bills its services not to the court but to the defendant, a policy that helps explain its appeal to cash-starved municipal governments. If these defendants then fail to pay their debts to the company, they can end up in jail. According to the film, that's where Wood may be headed.

Wood paid $10 toward the ticket, but the money went straight to JCS, knocking her fee down to $35 without making a dent in the original $41 dollar seat belt fine. The next month, she paid another $10 dollars, but the fine stayed the same.

Each month, the fees went up. By the end of the year, she owed the company nearly $300, more than seven times what she had owed -- and couldn't afford to pay -- in the first place. When the filmmakers caught up with Wood, she said she was getting ready to go to court, where she would be required to pay the full $300 fee, plus the original $41 ticket. "I'm gonna have to figure out how to come up with half of it right there," she said. "And I cannot leave the building till I do, or I will get locked up."

JCS didn't respond to requests for comment from The Huffington Post Tuesday afternoon. On its website, the company assures defendants that its officers are "trained in tolerance and equal opportunity. Nobody will be 'out to get you' and many probationers eventually end up appreciating their contact with the probation officers."

According to government data gathered by Human Rights Watch, hundreds of thousands of people are sentenced to probation with private companies in the United States each year. It's unclear how many are jailed for failure to pay their debts to these businesses.

In an interview with HuffPost, Daniel Evans, an attorney in Birmingham, Alabama, called the company's strategy a "horribly flawed business practice that sounds attractive to these municipalities because it allows them to save money."