Intervention

[A]llowance or disallowance of a motion for intervention rests on the sound discretion of the court after consideration of the appropriate circumstances. Rule 19 of the Rules of Court is a rule of procedure whose object is to make the powers of the court fully and completely available for justice. Its purpose is not to hinder or delay but to facilitate and promote the administration of justice. Thus, interventions have been allowed even beyond the prescribed period in the Rule in the higher interest of justice. Interventions have been granted to afford indispensable parties, who have not been impleaded, the right to be heard even after a decision has been rendered by the trial court, when the petition for review of the judgment was already submitted for decision before the Supreme Court, and even where the assailed order has already become final and executory. In Lim v. Pacquing (310 Phil. 722 (1995)], the motion for intervention filed by the Republic of the Philippines was allowed by this Court to avoid grave injustice and injury and to settle once and for all the substantive issues raised by the parties.

In Collado v. Court of Appeals, this Court reiterated that exceptions to Section 2, Rule 12 could be made in the interest of substantial justice. (STRADCOR v. Radstock, G.R. No. 178158, 4 December 2009)