61 Pa.C.S. § 1164

Where an inmate is in a State correctional institution either because of the inmate's sentence pursuant to the inmate's conviction or plea of guilty to a criminal charge or because of a commitment issued by any court of the Commonwealth having jurisdiction and, while so confined, the inmate commits a criminal offense and is subsequently convicted or enters a plea of guilty, the expenses of keeping the inmate in any State correctional institution pursuant to such subsequent conviction or plea of guilty shall be borne by the Commonwealth.