I think some greedy corporation would make its own line of synthetic workers, and would deliberately mark them with an obvious, hard-to-remove mark identifying them as such. And, since the corporation created its own workers, it would argue that the workers are its own property and therefore not have to pay them for their own services, leading to free labor. Human workers would make an outcry, about being replaced by machines (Hell that argument is already happening). Human-rights activists would argue that the synthetic workers are human-like, therefore they must be treated equal to humans. There would probably be a socio-comparison to the synthetic workers as slaves, leading to people bringing up the Civil Rights Movement and the abolition of slavery.