Vanita Gupta, head of the Civil Rights Division, at her office at the Justice Department in Washington on March 16, 2015. (Melina Mara/The Washington Post)

EACH YEAR in Virginia, state courts order license suspensions for 300,000 to 400,000 drivers, many of them indigent, who have failed to pay court costs — fines and fees stemming from convictions. Some 900,000 suspensions were in effect last year. That means roughly a sixth of the commonwealth’s motorists have lost their driving privileges because they were unwilling or, perhaps more frequently, unable to pay fines and fees.

The fines and fees may be levied for serious crimes, but in many cases they are not. According to the Virginia Department of Motor Vehicles, about two-thirds of the license suspensions were the result of unpaid costs for motor vehicle convictions — in other words, traffic tickets.

That’s a snapshot of a larger, national problem on which the Obama administration’s Justice Department is focusing: the proliferating practice of state and municipal courts imposing crippling fines that, when unpaid, can trigger jail time — a cycle Attorney General Loretta E. Lynch has called “the criminalization of poverty.” In the course of seeking to coerce payment, often mainly to generate revenue for state and local coffers, many courts are using arrest warrants and license suspensions. That in turn can lead to job loss or severe strains on families while doing little or nothing to promote public safety.

In a letter this week to local courts in all 50 states, the Justice Department put judges on notice that slapping fines and fees on defendants without regard for their ability to pay can be a constitutionally dubious practice. In some instances, it has relegated judges and police to roles that have little to do with justice and protecting the public, and more to do with filling the public coffers.

An egregious example was documented in 2014 by The Post’s Radley Balko, who showed that some of the dozens of municipalities in St. Louis County, Mo., derived more than 40 percent of their revenue from fines and fees levied by local courts. Most of the costs arose from traffic offenses, but, as Mr. Balko wrote, they also stemmed from fare-dodging on the local light-rail system, noise ordinance violations, zoning infractions including unkempt property and uncut grass, trespassing, disturbing the peace — even wearing “saggy pants.”

In the Justice Department letter, Vanita Gupta, head of the Civil Rights Division, and Lisa Foster, director of the Office for Access to Justice, wrote of the imposition of unchecked court costs that “in addition to being unlawful, to the extent that these practices are geared not toward addressing public safety, but rather toward raising revenue . . . can cast doubt on the impartiality of the tribunal and erode trust between local governments and their constituents.”

The officials urged courts to adhere to basic constitutional principles, warning them not to jail poor people who failed to pay court costs because they couldn’t afford it, and to consider alternatives such as community service for indigent defendants. Judges were also cautioned not to keep poor defendants in jail solely on the basis of their inability to post bail and not to make payment of court costs a condition of access to judicial hearings.

In the letter, the Justice Department stopped short of threatening to prosecute. But the implication was clear: Poverty itself is not a crime, and courts that treat it as such may themselves be trampling on the Constitution.