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WASHINGTON — The Justice Department is discouraging state court systems from jailing defendants who fail to pay fines or fees, warning against practices that it says run afoul of the Constitution and erode community trust.

A letter being sent Monday by the federal government to state court administrators makes clear that judges should consider alternatives to jail for poor defendants who don't pay their fines. It also says defendants should not be locked up without a judge first establishing that a defendant who failed to pay did so willfully.

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The memo comes out of a December meeting involving judges, court administrators, prosecutors and others to discuss improvements in how court fees and fines are assessed.

The new guidance comes amid concerns that some local courts are effectively punishing poor people for their poverty by imposing crippling fines and fees that, when unpaid, can result in jail time. That practice was exposed last year in a scathing federal report on the Ferguson, Missouri city government in which the Justice Department concluded that the municipal court prioritized revenue over safety and routinely issued arrest warrants to residents who had failed to pay fines for petty offenses.

Attorney General Loretta Lynch, joined by Principal Deputy Assistant Attorney General Vanita Gupta speaks during a news conference at the Justice Department in Washington, Wednesday, Feb. 10, 2016, about Ferguson, Missouri. Carolyn Kaster / AP

Though the state court system operates independently of the Justice Department, the memo is intended to put local judges on notice that ordering jail time for unpaid fines can violate federal law, open the door to constitutional challenges and trap residents in a cycle of escalating debt, unnecessary incarceration and unemployment.

"Furthermore, in addition to being unlawful, to the extent that these practices are geared not toward addressing public safety, but rather toward raising revenue, they can cast doubt on the impartiality of the tribunal and erode trust between local governments and their constituents,' reads the letter from Vanita Gupta, the head of the Justice Department's Civil Rights Division.

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The letter also says courts must give defendants adequate notice when enforcing fines or fees, should not use arrest warrants to coerce the payment of court debt and should not impose bonds that a defendant has no ability to pay.

Also Monday, the Justice Department was announcing $2.5 million in competitive grants to state and local governments that want to explore changes in how court fees and fines are assessed and enforced.