Rules on Civil Procedure
Section 7. Compulsory counterclaim. - A compulsory counterclaim is one which, being cognizable by the regular courts of justice, arises out of or is connected with the transaction or occurrence constituting 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. Such a counterclaim must be within the jurisdiction of the court both as to the amount and the nature thereof, except that in an original action before the Regional Trial Court, the counter-claim may be considered compulsory regardless of the amount. (n)