Part of the reason unions work is because they sign agreements with employers that prevent them from hiring from outside the union to fill jobs during a strike.

Part of the reason unions work is because they sign agreements with employers that prevent them from hiring from outside the union to fill jobs during a strike. I can't imagine a scenario in which Uber enters such an agreement. Even if a union exists, Uber is free to hire non-union members and pay them as much as necessary to get them to work during a strike. In the long run, economics wins out and Uber ends up paying the minimum that enough people are willing to work for, which is exactly what they were doing anyway.