I think you're confused. It's definitely not illegal in any state to have informal political discussions with coworkers. Maybe what you're referring to is that it's illegal for employers to tell employees to vote a certain a way or retaliate against them for holding certain political views.
Only in some states is this legally protected. If a private company allows it, then there is no problem.
However, most private companies don't allow political discussion and it's not illegal to control this unless you live in certain states, California being one of them.
