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A federal lawsuit filed Thursday by a civil rights group alleges a private company used the threat of jail to extort money from poor residents in rural Alabama who did not keep up with court fines.

The Southern Poverty Law Center's complaint accuses Judicial Correction Services, the largest private probation company in Alabama, of violating federal racketeering laws during its efforts to collect fines on behalf of the Clanton, Alabama municipal court.

“We’re bringing this lawsuit because this simply has to stop,” said Sam Brooke, an SPLC attorney. “JCS cannot be permitted to continue operating this racketeering scheme that is extorting money from the impoverished individuals under the threat of jail.”

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The practice is not new. In 2012, an NBC News investigation found the court in Augusta, Georgia, routinely jailed those who failed to pay their fees to a private probation company.

But the SPLC lawsuit comes amid growing scrutiny of the practice of issuing arrest warrants for failing to pay court fines, which was heavily criticized in the scathing Department of Justice report on Ferguson, Missouri released last week.

In addition to finding a pattern of racial bias by police and officials, the DOJ said the Ferguson municipal court routinely issued arrest warrants “not on the basis of public safety needs, but rather as a routine response to missed court appearances and required fine payments.” The report found the court “made this penalty even more onerous by only allowing the suspension to be lifted after payment of an owed fine is made in full” and “added charges, fines, and fees for each missed appearance and payment.”

Advocates and attorneys say the growing for-profit probation industry encourages similar practices in municipal courts across the south.

“Even though the U.S. Supreme Court has ruled very clearly that a person’s probation can’t be revoked and they can’t be locked up simply because they genuinely can’t afford to pay fines, let alone private probation fees, that’s often just thrown to the winds,” said Chris Albin-Lackey, a senior researcher at Human Rights Watch, which issued a 2014 report on the probation industry.

Probation companies contract with courts to supervise people convicted of low-level fines and insure they pay court debt. On top of their court fines, probationers must pay a “supervision fee” to the company, typically between $20 and $40 per month. Though often attractive to cash-strapped municipalities, many say this “offender-funded” model traps poor defendants in a cycle of debt, and can land them in jail if they do not pay.

Suits against JCS and other probation companies are ongoing in several municipalities, including DeKalb County, Georgia and Shelby County, Alabama. JCS did not immediately respond to request for comment from NBC News.

Georgia could soon force a change to the industry. A bill currently moving through the state legislature would impose widespread reforms on the industry in the state, where 80 percent of people on probation for a misdemeanor conviction are supervised by private companies.