A career limiting move is an action which can get you in trouble with your employer, or otherwise decrease your success at work. It generally refers to something you contemplate doing even though you know it's a bad idea.
For example, if your boss asks you to pass him some sugar in the break room while getting himself some coffee...you might contemplate saying "Sure, here ya go fat ass." But that would be a career limiting move, and you should instead just say "okay."