Jurisdiction over an intervention is contingent upon the court's jurisdiction over the main action; an intervention is ancillary and supplemental, not an independent proceeding, and thus ceases to exist when the main case is dismissed, particularly on jurisdictional grounds.

The dispute originated from the Municipal Assessor of Mauban, Quezon's assessment of substantial realty taxes on the Mauban Plant, a power generation facility owned by QPL, based on a market value of approximately P29.6 billion. QPL contested this assessment, declaring a much lower value of about P15 billion, and tendered a significantly smaller amount as its first quarter installment for realty taxes, which was rejected by the Municipal Assessor.

• The Municipal Assessor of Mauban, Quezon assessed QPL's power plant machinery and buildings at a market value of P29,626,578,291.00 in 1999, resulting in annual realty taxes of around P500 Million.
• QPL contested this, declaring the property value at only P15,055,951,378.00 in a sworn statement filed in May 2000.
• In March 2001, QPL tendered P60,223,805.51 as the first quarter realty tax installment for 2001 based on its declared value, but the Municipal Assessor rejected the payment.
• QPL filed a Complaint for Consignation and Damages (Civil Case No. 0587-M) before the RTC, depositing the rejected amount and challenging the Municipal Assessor's authority and valuation process.
• Frumencio E. Pulgar, alleging interest as a resident and taxpayer, filed a Motion for Leave to Admit Answer-in-Intervention in January 2002, which was initially admitted by the RTC.
• In June 2002, QPL and the Province of Quezon agreed to submit their dispute to the Secretary of Finance, who subsequently issued a resolution on the matter in August 2002.
• The RTC, in its Order dated December 2, 2002, dismissed QPL's complaint (Civil Case No. 0587-M) for lack of jurisdiction, finding it was essentially a protest against the assessment amount which required payment under protest and appeal to the Local Board of Assessment Appeals (LBAA), not the RTC.
• Consequently, the RTC also dismissed Pulgar's intervention, reasoning that it could not stand alone following the dismissal of the main case.
• Pulgar's motion for reconsideration was denied by the RTC in its Order dated March 13, 2003.

• Pulgar argued that as a resident and taxpayer of Quezon Province, he had a legal interest in the collection of realty taxes from QPL.
• Pulgar asserted that even if the RTC lacked jurisdiction over the main case, the Supreme Court should still review the correctness of the Municipal Assessor's realty tax assessment against QPL.
• Pulgar included a counterclaim for moral damages and attorney's fees based on alleged environmental disturbance caused by QPL's power plant.

• QPL (original plaintiff) argued that the Municipal Assessor lacked legal authority for the assessment and failed to comply with the prescribed valuation process.
• The original defendants (Province of Quezon, Municipal Assessor, Municipal Treasurer, Provincial Assessor, Provincial Treasurer) argued that QPL was estopped from denying the Municipal Assessor's authority as it had previously paid taxes based on the latter's assessment.
• The RTC (in its ruling) effectively argued that it lacked jurisdiction because QPL's complaint was a tax protest that did not comply with the requirement of payment under protest and appeal to the LBAA.

• Whether the RTC erred in dismissing petitioner Pulgar's motion for intervention as a consequence of the dismissal of the main case (Civil Case No. 0587-M) due to lack of jurisdiction.

• The Supreme Court denied Pulgar's petition, finding no merit in it.
• The Court affirmed the RTC's dismissal of the intervention, reiterating that intervention is not an independent action but is ancillary and supplemental to the main litigation.
• Since the RTC correctly dismissed the main case filed by QPL for lack of jurisdiction (as it was essentially a tax protest improperly filed without payment under protest and should have been brought before the LBAA), the intervention necessarily lost its basis.
• An intervention presupposes a pending suit in a court of competent jurisdiction; without a valid main action, the intervention cannot survive.
• The Court declined Pulgar's request to review the correctness of the tax assessment, as the dismissal was based purely on the procedural ground related to the nature of intervention following the main case's dismissal for lack of jurisdiction.

• Ancillary Nature of Intervention — Intervention is a proceeding by which a third person is permitted to become a party to an action or proceeding between other persons for the protection of some right or interest alleged by the intervenor to be affected by such proceedings. It is never an independent action but is ancillary and supplemental to the existing litigation, requiring a pending suit in a court of competent jurisdiction. It was applied here to rule that since the main case (QPL's complaint) was dismissed for lack of jurisdiction, Pulgar's intervention, being merely ancillary, could not stand independently and was thus correctly dismissed.

• "[I]ntervention is never an independent action, but is ancillary and supplemental to the existing litigation. Its purpose is not to obstruct nor x xx unnecessarily delay the placid operation of the machinery of trial, but merely to afford one not an original party, yet having a certain right or interest in the pending case, the opportunity to appear and be joined so he could assert or protect such right or interests."
• "Otherwise stated, the right of an intervenor should only be in aid of the right of the original party. Where the right of the latter has ceased to exist, there is nothing to aid or fight for; hence, the right of intervention ceases."

• Asian Terminals, Inc. v. Judge Bautista-Ricafort (536 Phil. 614 (2006)) — Cited to support the principle that intervention presupposes the pendency of a suit in a court of competent jurisdiction.
• Cariño v. Ofilada (G.R. No. 102836, January 18, 1993, 217 SCRA 206) — Cited to emphasize that intervention is ancillary and ceases when the right of the original party (in the main action) ceases to exist.