(a) General rule.--Except as otherwise provided in section 5424 (relating to temporary emergency jurisdiction), a court of this Commonwealth may not exercise its jurisdiction under this subchapter if, at the time of the commencement of the proceeding, a proceeding concerning the custody of the child has been commenced in a court of another state having jurisdiction substantially in conformity with this chapter unless the proceeding has been terminated or is stayed by the court of the other state because a court of this Commonwealth is a more convenient forum under section 5427 (relating to inconvenient forum).

(b) Stay; communication with other court.--Except as otherwise provided in section 5424, a court of this Commonwealth, before hearing a child custody proceeding, shall examine the court documents and other information supplied by the parties pursuant to section 5429 (relating to information to be submitted to court). If the court determines that a child custody proceeding has been commenced in a court in another state having jurisdiction substantially in accordance with this chapter, the court of this Commonwealth shall stay its proceeding and communicate with the court of the other state. If the court of the state having jurisdiction substantially in accordance with this chapter does not determine that the court of this Commonwealth is a more appropriate forum, the court of this Commonwealth shall dismiss the proceeding.

(c) Modification.--In a proceeding to modify a child custody determination, a court of this Commonwealth shall determine whether a proceeding to enforce the determination has been commenced in another state. If a proceeding to enforce a child custody determination has been commenced in another state, the court may:

(1) stay the proceeding for modification pending the entry of an order of a court of the other state enforcing, staying, denying or dismissing the proceeding for enforcement;

(2) enjoin the parties from continuing with the proceeding for enforcement; or

(3) proceed with the modification under conditions it considers appropriate.