Most likely, it would be a legal zoom like company that allows you to easily form your own LLC, elect for c corp tax filing status and then generate invoices and send to the companies that hired you.

So you mean an temping agency? Those usually work with 0 hour contracts while people are on call and rented out.

Great! Let's get a whole structure setup, so that these people who can hardly make ends meet as-is now have to worry about a whole extra structure to establish, and pay money for!