The US find slavery perfectly acceptable - it's right there in the constitution

> Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.

All you need to do is jail them and there is your slave workforce.

> [Our nation incarcerates more than 1.2 million people in state and federal prisons, and two out of three of these incarcerated people are also workers. But there are two crucial differences: Incarcerated workers are under the complete control of their employers, and they have been stripped of even the most minimal protections against labor exploitation and abuse. Nationally, incarcerated workers produce more than $2 billion per year in goods and more than $9 billion per year in services for the maintenance of the prisons.] (https://www.aclu.org/news/human-rights/captive-labor-exploitation-of-incarcerated-workers)