I could be a server who works shifts at two restaurants. They both call me the same morning with available shifts that day. I pick the one that usually gives better tips. I’m still an employee of both.
Edit: Guess the Uber shills don’t like it and downvoting is easier than admitting you’re wrong.
This breaks not one but two of the site guidelines. Would you please (re-)read them and not do that? https://news.ycombinator.com/newsguidelines.html
For uber/lyft that's not rare at all, that happens multiple times a day if you want to extend the shift analogy to giving someone a ride.
And again these are irrelevant details. The point remains solid.
The reason you are an “employee” and not a “contractor” at the restaurants is because they dictate your hours and place of business.
Your example about filling in is a red herring as by its nature it’s an atypical circumstance.
These arguments are ridiculous.