My employer called me into work under the pretense "to talk" when I was on LOA before my release date from the doctor. My employer then proceeded to terminate my employment for job performance, however, refused to prvide any specific details. Can they legally even speak to me before my return to work date and do I have a basis for a law suit?

... Can they legally even speak to me before my return to work date and do I have a basis for a law suit?

Of course your employer can call you when you are on leave. Anyone who knows your number can. If you don't want to talk, then don't answer the phone.

And no, you don't have a basis for a lawsuit. In most if not all places, employment is "at will". Your employer doesn't need a reason to let you go.

What type of leave of absence ? Was it company paid ? Did you apply though any federal leave program ?
Was there work performance issues ( really) before you went on leave ?

But most likely they can, in some cases they have to wait till you come back from leave and then fire you.

You had no obligation to go in and talk to them, that was your choice

Did you have a union or employment contract? What State?

I agree that, if you are an at will employee, you can be terminated for no reason. However, your employer gave cause, performance, so you may have more options. Please answer everyone's questions and also surf your state's Fair Labor Board so see if you have been wronged.