Still, have you ever heard the song "Sixteen Tons?"[1] You might recognize the lines "another day older and deeper in debt" and "I owe my soul to the company store." It's about the life of a coal miner in Kentucky. Those lines refer to a system where the company paid its workers in vouchers that they could use to buy food and clothing from the company store. Prices at the company store were higher than the workers could afford on the wages they received, but since they didn't get cash they didn't have the option to buy elsewhere. So they'd buy on credit and gradually build up a debt to the company that they had no way to pay off.
Is that slavery? Perhaps not technically, since the workers weren't owned by the company and couldn't be sold. But they didn't have many choices, either. They were basically stuck doing a fixed amount of work each day in exchange for food and lodging. Sounds an awful lot like slavery in practice.
[1] Obligator wikipedia link - https://en.wikipedia.org/wiki/Sixteen_Tons
