A pleading shall state as a counterclaim any claim which at the time of serving the pleading the pleader has against any opposing party, if it arises out of the transaction or occurrence that is the subject matter of the opposing party’s claim and does not require for its adjudication the presence of third parties of whom the court cannot acquire jurisdiction. However, such a claim need not be stated as a counterclaim if at the time the action was commenced the claim was the subject of another pending action.
Puerto Rico Legal Code