Story highlights Among the practices Justice Department officials are trying to stop is the use of court fines and assessments as a source of revenue

DOJ calls for courts to first establish that nonpayment is willful and not just the result of indigence

Washington (CNN) The Justice Department issued new guidelines to state and municipal court systems aimed at preventing indigent defendants from being jailed because they're too poor to pay fines for minor infractions.

The legal guidance is "intended to address some of the most common practices that run afoul of the United States Constitution and/or other federal laws," according to a letter sent Monday to chief justices and court administrators around the nation from Vanita Gupta, head of the Justice Department's civil rights division, and Lisa Foster, director of the Office for Access to Justice.

Among the practices Justice Department officials are trying to stop is the use of court fines and assessments primarily as a source of revenue by some municipalities.

The widespread practice gained attention in the wake of riots in Ferguson, Missouri, in 2014.

A Justice Department investigation, sparked by the police shooting of Michael Brown, found unconstitutional racially biased practices by the Ferguson police and city court system, which sometimes jailed people because they failed to pay traffic and other low-level fines.

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