Another perspective: in some states, such as Pennsylvania, employment by law is "at will" and you can be fired/sacked/relieved "without cause."

So you might lose your job. You'll get a reference but nothing that your future employer is really going to base a hiring decision on.

I'm not convinced that the old employer loses any money by replacing and retraining employees once you subtract raises that would have been earned and benefits, so I tend to think there's still a tremendous amount of power on the side of the company rather than the employee.