IMO this is different from discriminating based on political opinions because it's the employee who decides whether they want to leave. Similarly, if you build a company and are very vocal on Twitter supporting a presidental candidate, you will probably mostly attract people who support the same — but again, it's the choice of the employee. Very different from asking candidates about who they voted for and then tossing resumés based on that.
It's asymmetric, but laws should generally be in favor of the employees, because the employers already have most of the power on their side.
It's asymmetric, but laws should generally be in favor of the employees, because the employers already have most of the power on their side.