The U.S. Constitution guarantees equal protection under law. So why do we tolerate a system in which people with money go home after being convicted of a crime while the poor go to jail for the same offense?

The difference is the ability to pay a fine. One defendant can write a check, while the other may have to work off what he owes at the rate of $5 a day incarcerated. The underlying offense may be exactly the same, but the difference between freedom and months in jail can be the balance of a bank account.

This is not a theoretical problem. Research by the American Civil Liberties Union of Maine determined that nearly 10 percent of inmates booked into the Cumberland County Jail between August 2013 and August 2014 were there solely on a warrant for failure to pay fines or court-ordered restitution. Of the 10,674 people booked during that period, 909 were arrested just for failing to pay court debts.

Court officials claim that no one is in jail just because he is poor, but that is a legal fine point. Judges set up what are supposed to be affordable payment plans at sentencing, and anybody who keeps up with the schedule, rich or poor, will not be arrested. But once they fall behind, people with resources can pay their way out and those without cannot.

This is not only a matter of fairness, it is one of common sense. It costs the state far more to work off the fines through incarceration than it would to collect them.

That money would be much better spent getting former convicts off drugs and into jobs than it is warehousing them in jail and then releasing them to re-offend.

In the last four months of last year, 41 inmates were sentenced to pay off back fines or restitution in Cumberland County. Thirteen were unable to pay off enough to be released and paid their debt by sitting in jail. The cost to the county to house them for a total of 232 days was $25,990. The amount of fines and restitution recouped was $10,489.

Jailing offenders is not the only way to impose meaningful consequences for breaking the law, but it is the most expensive. Nonviolent offenders who are not a threat to public safety can work off their debts outside the walls of a jail. People with substance abuse disorders don’t often recover without treatment. Paying for that would be a much more effective use of public resources.

If people want to insist that failing to pay court-ordered fines should be punished by jail time, then they should insist that everyone be treated the same, rich or poor. If one set of offenders has to work off a fine at $5 a day in jail, then the other group shouldn’t be able to pay its way out.

A better approach would be finding solutions outside the jail walls for both groups of offenders.