You dont. People all around the world are in various ways economically enslaved. Its just that in western countries we have rules in place to limit what you could contractually mandate from an employee. You can report unsafe working conditions, long hours, unreasonable pay or discrimination based on immutable characteristics. Usually you report this to your boss, if he doesn't listen then you report it to an independent organisation to arbitrate, if this doesn't work then you have courts, social media and governments to rely on. If all else fails you could quit your job at no repercussions and find a new one.
its just that all of methods above are useless if the organisation has close ties to all of these pathways of resolution.