A bipartisan group of senators unveiled a comprehensive proposal on Thursday that would reduce federal prison sentences for nonviolent drug offenders and seek to cut down on recidivism.

The bill would be among the most significant criminal justice reform legislation in decades. It comes as support for reform has been growing on both sides of the aisle, both because of the overwhelming financial burden of mass incarceration and a push among legislators towards rehabilitation rather than punishment for drug offenses.

The bill’s major provisions would:

• Reduce enhanced mandatory-minimum sentences for repeat drug offenders, including removing mandatory life sentence for three-strike offenders.
• Limit offenses that trigger mandatory minimums to serious drug felonies.
• Offer more discretion for judges to sentence low-level offenders below the 10-year mandatory minimum.
• Limit — though not prohibit — solitary confinement for juveniles in federal custody.
• Allow some nonviolent juveniles to seal or expunge their convictions.
• Apply several sentencing reforms retroactively.
• Require the Bureau of Prisons to come up with research-based programs to reduce recidivism.

The bill doesn’t do away with mandatory minimum sentencing entirely, something that a full 77 percent of Americans say they support. The federal prison population has boomed over the past 30 years, from 24,600 in 1980 to more than 200,000 last year, in part because of mandatory minimum sentencing for drug offenses.

The bill also introduces new mandatory minimum sentences for other crimes, such as violent felonies, some violent firearm offenders, those who commit interstate domestic violence or provide weapons or other materials to terrorists.

That’s one critique of the bill from some reform advocates, who say that minimum sentences are costly and mostly end up targeting low-level, nonviolent offenders.

“We believe that punishments must fit the crime and that a cookie-cutter approach too often gets in the way of justice,” said Anthony Romero, executive director of the American Civil Liberties Union, in a statement.

The senators said the bill would impact at least 6,500 people in the federal prison system. The bulk of the roughly 2.2 million people who are incarcerated today are in state prisons and jails.

Molly Gill, government affairs counsel for Families Against Mandatory Minimums, said the bill could go further, but added: “There’s going to be a lot of families who will benefit from this law and a lot of people who are going to get a lot of years back.”

The bill still must pass the Senate before moving to the House of Representatives for consideration. The White House hasn’t yet weighed in on the bill, but President Barack Obama has repeatedly called for comprehensive criminal justice reform.

Related film: Prison State

An intimate look at the cycle of mass incarceration in America and one state’s efforts to reverse the trend.

Sarah Childress, Former Series Senior Editor, FRONTLINE