An unusual coalition of conservatives and liberals in Congress is working toward reforming prison sentencing, particularly mandatory minimum sentences, which have put thousands behind bars for nonviolent, usually drug-related crimes.

The issues creating rare bipartisanship are the high costs of mass incarceration as well as the human toll and unfairness of automatic sentences.

For many on the right, the main issue is money — prison populations have exploded in recent decades, straining state and federal budgets. Federal prisons today hold about 220,000 prisoners, up from about 25,000 in the 1980s. It’s no coincidence that the 1980s gave birth to mandatory minimum sentences and “three-strikes” rules. After well-publicized stories of lenient sentences for violent crimes, public sentiment backed a “tough on crime” approach — and politicians gave the voters what they wanted. No politician, Republican or Democrat, wanted to be labeled soft on crime.

Another little-known factor in the tough-sentence movement was the prison guard union, particularly in California, where union money pushed “three-strike” laws because more inmates meant building more prisons, hiring more prison guards — and, consequently, more union members paying dues.

Calling for sentencing reform, U.S. Attorney General Eric Holder said, “Too many Americans go to too many prisons for too long, and for no truly good law enforcement reason.” Of the 220,000 federal prisoners, about half are serving time for nonviolent drug offenses.

In the federal prison system, money is also an issue. In the later 1990s, the Department of Justice spent about 13 percent of its budget on the Bureau of Prisons. In 2013, prisons took about 25 percent of the department’s budget — or $6.4 billion.

For those of the left, the key driver in sentencing reform is fairness and the human cost of throwing people in prison for dozens of years for nonviolent crimes. Congressional testimony revealed anecdotal reports of injustice: a man serving a 55-year-sentence for selling $350 worth of marijuana, while another man convicted of second-degree murder serving 22 years — both sentences imposed by mandatory sentencing rules, which don’t give judges leeway.

The “lock them up and throw away the key” attitude of mandatory sentences and so-called “three-strikes” rules have taken judges, often justice itself, out of the courtroom.

Seeing the unfair consequences of mandatory sentences , conservative Sen. Rand Paul, R-Kentucky, said, “There is no justice here. It is wrong and it needs to change.”

An Associated Press article in Monday’s Butler Eagle pointed out that changing the mandatory sentencing laws has support from tea party conservatives and liberal leaders in Congress.

In addition to sometimes inhumane punishment for minor drug offenses, many elected officials see excessive incarceration as a burden on taxpayers. Beyond costing billions of dollars, the focus on drug-related crimes misdirects financial and law enforcement resources away from more important crimes. Most experts believe prisoners serving time for drug-related, nonviolent crimes are better served with treatment and alternative forms of punishment, such as electronic monitoring. And this approach would cost far less than the $30,000 to $40,000 a year it costs to house a prisoner.

With Democrats and Republicans agreeing on the need to reform sentencing laws, congressional action reducing incaceration and reforming mandatory sentencing laws could be a rare accomplishment in gridlocked and partisan Washington, D.C.