The constitutions of all 50 states prohibit private militias. That prohibition in Pennsylvania reads “No standing army shall, in time of peace, be kept up without the consent of the Legislature, and the military shall in all cases and at all times be in strict subordination to the civil power.” (PA Constitution art. I Section 22).
In 29 states, including Pennsylvania, criminal statutes also prohibit paramilitary activity carried on without the authority of the civilian government. (18 PA Cons. Stat. Ann. Section 5515). Legal militias defend the United States or any individual state, as described in the PA Constitution Title 51, Part II, “PA National Guard, PA Guard and Militia.”