State tax filing

I literally do not understand how states get away with this. 

 

"If your employment agreement provides the employee with a physical workspace at the employer’s Pennsylvania location and the employee elects to perform their work outside of Pennsylvania, then the income for that employee is allocated to Pennsylvania."

So my employer doesn't require me to work in PA, but allows me to work remotely in TN full time, I still have to pay taxes because its not a "requirement" that I work remotely. They justify I can relocate and work in the office. So in that case I'm paying tax to a state I don't reside in. TN doesn't have any state income tax so I guess that is nice otherwise it sounds like I would pay tax in both states. 

So I will not get tax credits or a full refund from PA and the city of philly because its not "required" by my employer that I work remotely?