Katrina is correct. As a freelancer myself, we work for ourselves, not UpWork. UpWork is just the middle man - the company that brings clients and freelancers together. That's it. It's like any other freelancing website. If you live in the US, then think of it as a kind of Craig's list, with added features, securities, and rules of use. There are rules for clients and rules for freelancers. If a freelancer doesn't follow the rules, their account can get locked or banned altogether, just as with a client who breaks the rules. Clients don't work for UpWork. They are the job/project posters. Likewise, freelancers don't work for UpWork.
Except you're wrong... UpWork provides absolutely no transparency from the employer but requires proof of identity and full exposure for the freelancer. That's not a middle man, that's micro-management in favor of the employer.