Maybe it should, but it doesn't. There's nothing an employer can do that violates the Constitution because the Constitution is a limitation on governmental actions, not private actions.
Possibly not, but the Federal Government is in place to protect our rights period.
Be that against an employer or another government entity, it is the job of our Government to secure our rights.
An Employers rights end where my (and your) bumper begins.
Anything other than that is a matter for the courts to decide.
Semper Fi