They aren't mandatory everywhere, atleast in germany.
You can join the union or not. If you don't join you can still take advantage of the union negotiated rates or not if you wish. If you think you can negotiate better than the union you're still free to do so.
You can join the union or not. If you don't join you can still take advantage of the union negotiated rates or not if you wish. If you think you can negotiate better than the union you're still free to do so.