Fired

What is the name of your state (only U.S. law)? Pennsylvania. Can an employer legally fire you when you are not clocked in?

You may be fired for any reason or no reason at any time.

Can an employer legally fire you when you are not clocked in? Of course.

You can be fired *at any time* for any reason except a reason prohibited by law (ie age, religion, gender) or unless you have a binding employment contract to the contrary.

That's at-will employment. (You can google it.)