In 1983, the Supreme Court ruled that if someone is too poor to pay a fine, jailing them violates federal law. But Monday’s letter hinted that not all courts are following that ruling.

Such a recommendation to courts from the Justice Department is rare. The last the department wrote a similar letter was in 2010, when it reminded state courts they were required, and legally obligated, to provide court interpreters to non-English speakers (that concern led to investigations in Colorado and North Carolina).

Last December, the White House held a two-day conference with prosecutors, defense attorney’s, judges, and scholars, to discuss the growing trend of courts turning into moneymakers for their cities. This was also the focus of a lawsuit filed in February by the Justice Department against Ferguson, Missouri, the city where Michael Brown, an 18-year-old unarmed black man, was shot and killed by a white police officer in August 2014. In that suit, the Justice Department said officers in Ferguson used racist and discriminatory “patterns and practices” of policing that targeted black people, and where, The New York Times wrote, “investigators concluded that the city’s police department and court operated not as independent bodies but as a moneymaking venture to pad Ferguson’s budget.”

The Justice Department has also raised concerns about jurisdictions that partner with private, for-profit companies to run their probation programs. In this type of system, the company collects a monthly payment from individuals to pay for its own services, on top of the fines they owe to the court. About a dozen states use a system like this, according to a Human Rights Watch report from 2014. The report argued that this system treats the wealthy and poor unequally, because someone who can afford to pay their fine off in a single payment will end up paying much less than a person who can’t afford to do so. Probation companies make their profit from monthly charges in “supervision fees,” so the longer it takes to pay off a fine, the more money the person pays the company.

Take the example of Greenwood, Mississippi, a small Delta town of 15,000. In early 2013, the Human Rights Watch report said a private company contracted to run the town’s probation program. Less than a year after the program began, nearly 10 percent of the people in town owed fees to the company. The report estimated that the company collected about $21,500 in fines each month for the town, and by charging each person on probation $40 in monthly fees, the company could have pulled in $48,000 each month. It wasn’t long before the town, where the average person made just $14,000 each year, dumped the program. Wayne Self, who served on the county’s board of supervisors, told Human Rights Watch the company made work for itself “off the backs of the poor people.”