The use of prison labor, and its meager compensation, has long been a contentious issue. But while it is private prisons that get a lot of media attention for their for-profit business model, wages for the incarcerated in public and federal prisons, which hold the vast majority of inmates, have declined over the past two decades.

Data compiled by the Prison Policy Initiative shows that the average incarcerated worker in state and federal prison now earns 86 cents per day, a 7 cent decrease from 2001 when inmates earned 93 cents for a day’s work.

The nation’s incarceration rate has spiked as much as 500 percent in the last 40 years, driven in part by the War on Drugs and bipartisan “tough-on-crime” policies. While the prison population has skyrocketed, government funding for housing the prisoners has not kept up. That has forced the incarcerated to help pay for the high cost of their imprisonment through steep fees. Coupled with low or in some cases non-existent wages, that has left inmates in destitute conditions throughout their sentence.

“The cost of living goes up every year on the outside and they don’t just account for that in prison,” said Cole Dorsey, an organizer for the Incarcerated Workers Organizing Committee, an offshoot of the Industrial Workers of the World union.

Wendy Sawyer, a policy analyst at the Prison Policy Initiative, said it’s hard to pinpoint why wages have gone down, but James Kilgore, activist and author of “Understanding Mass Incarceration,” said the decrease reflects the punitive structure of the prison system and goes hand-in-hand with charging inmates co-pays for services — a “pay them less and make them pay more” scheme, according to Kilgore.

During the period studied, seven states decreased their maximum wages for “regular prison jobs,” jobs that are part of supporting the prison, such as custodial and maintenance work. South Carolina also moved away from paying inmates in this sector, joining six other states — Alabama, Arkansas, Florida, Georgia, Mississippi, and Texas — that only pay in rare circumstances.

Wages for prisoners have shaped the debate on inmates’ rights. Nearly a year ago, inmates at dozens of prisons organized a nationwide prison strike with labor reform and better pay at the center of their demands. Those calling for reform argued that prison labor is a profit-producing system and resembles “modern day slavery” allowed through the 13th Amendment, which abolished slavery “except as a punishment for crime whereof the party shall have been duly convicted.”

Kilgore said deregulation of the labor market and the implementation of certain tax codes and legislation, make it so that even if the clause was amended there would still be other ways to legally not pay incarcerated workers.

“The idea that all of a sudden Department of Corrections are going to turn around and pay everybody a minimum wage — that’s not going to happen,” Kilgore said. “The political and economic consequences of that are too great.”

Low wages are not the only concern around the exploitation of prisoners. The data collected by the Prison Policy Initiative for each state doesn’t account for deductions — fees like restitution or additional expenses such as stamps, paper, toiletries, supplementary food, or phone calls. The extra purchases and garnished money means prisoners receive a lot less than what they’re earning.

“Of course the people that are incarcerated are not generally people that are wealthy, but there’s still an attempt to squeeze as much as possible out of them and their family,” Kilgore said. “Otherwise, how are you going to justify charging people 50 cents a minute for a phone call?”

The United States has more than 2.2 million people incarcerated in federal and state prisons and county jails — the largest prison population in the world. According to the Bureau of Justice Statistics, the average annual state corrections cost per inmate in 2010 was $28,323, and a quarter of states spent $40,175 or more. As prisons have expanded, the cost of incarceration has increasingly been placed onto inmates and their families.

Consider the cost of medical co-pays in prison which many states charge. A $5 co-pay would take weeks to earn in some states, deterring inmates from seeking out medical care. In the most extreme cases, such as in Texas, inmates who seek medical services are charged a yearly co-pay of $100 while earning nothing.

“The system costs something around $80 billion a year and these are costs that we’re not actually willing to pay for,” said Chiraag Bains, a senior fellow at Harvard Law School’s Criminal Justice Policy Program. “We had severe budget crunches especially in the aftermath of the 2008 financial crisis. And so these costs are being passed on to people who are actually within the system — defendants, and prison and jail inmates.”

Prison wages are not likely to increase anytime soon. Inmates are not protected under the Fair Labor Standards Act and Attorney General Jeff Sessions has indicated that he plans to bring back the same “law-and-order” approach to criminal justice that laid the foundation of mass incarceration.