42 Pa.C.S. § 5913: Spouses as witnesses against each other.

Except as otherwise provided in this subchapter, in a criminal proceeding a person shall have the privilege, which he or she may waive, not to testify against his or her then lawful spouse except that there shall be no such privilege:

(1) in proceedings for desertion and maintenance;

(2) in any criminal proceeding against either for bodily injury or violence attempted, done or threatened upon the other, or upon the minor children of said husband and wife, or the minor children of either of them, or any minor child in their care or custody, or in the care or custody of either of them;

(3) applicable to proof of the fact of marriage, in support of a criminal charge of bigamy alleged to have been committed by or with the other; or

(4) in any criminal proceeding in which one of the charges pending against the defendant includes murder, involuntary deviate sexual intercourse or rape.