23 Pa.C.S. § 5423
Except as otherwise provided in section 5424 (relating to temporary emergency jurisdiction), a court of this Commonwealth may not modify a child custody determination made by a court of another state unless a court of this Commonwealth has jurisdiction to make an initial determination under section 5421(a)(1) or (2) (relating to initial child custody jurisdiction) and:
Cross References. Section 5423 is referred to in sections 5210, 5422, 5424, 5428 of this title.