“Free” workers under capitalism used to often not be free to leave the job. As in they’d be locked in, or some big dudes would encourage them to stay, or they’d be in some remote area and paid largely in scrip, and practically unable to quit, or a despotic local “big man” major employer would ensure they’d have to leave town if they upset him, which could include things like “wasn’t back in the bunk house before curfew”. The labor movement is largely the reason capitalists don’t/can’t still do those things.
