Compare it to requirements to file with financial and corporate regulators - there are, generally, more stringent requirements on public companies, but large privately-owned ones also have tax and reporting obligations that small ones don't. There's an intersection of different factors which determine what demands we make of a company, of which corporate status is prominent but not solely determinant. Size and turnover are other factors.
But do please note, the issue is not about exploitation, that's an inaccurate caricature. It's about a level playing field in bargaining. For small and large businesses that requires extremely different rules. Small businesses get less stringent rules in every area of corporate regulation, labour laws are the same.