A sweeping Associated Press investigation published Monday found that the supply chains for hundreds of popular food brands are tied to prison labor.

The AP reports that prisoners nationwide are forced to work dangerous agricultural jobs with little workplace protections – sometimes for pennies an hour, or no pay at all. The goods they produce are sold to private companies and end up in well-known consumer products, from Frosted Flakes to Coca-Cola.

KNX News Chief Correspondent Charles Feldman spoke to AP global investigative reporter Margie Mason, who co-authored the report.

“We spent the past two years gathering all kinds of records from Departments of Corrections all over the country,” Mason said. “We also went out on the ground and we did the work kind of following cattle, let's say, that was leaving the Louisiana State Penitentiary. We followed that to an auction house, and then onto a slaughterhouse, and we saw that that was entering the supply chains of companies like Mcdonald's and Burger King and Walmart, and also Cargill, which is the largest private company in the US.”

Mason said some of the companies were unaware that the goods they bought were sourced from prisons, but others openly admitted to it.

“We had companies such as Cargill, again, they came back and said, yes, we've been buying from prison farms in at least three states, and we're gonna take a look at this and decide whether or not to take action,” she said.

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While many companies involved, like General Mills and Whole Foods, have policies against using prison labor, it’s ultimately up to them whether they want to investigate and take action. Under the 13th Amendment, slave labor is legal as punishment for a crime.