The Senate or its committees may conduct inquiries in aid of legislation only in accordance with duly published rules of procedure; publication of such rules is mandatory for each Congress and failure to do so renders any such inquiry procedurally infirm and unconstitutional.

The "Hello Garci" tapes, allegedly containing a wiretapped conversation between then-President Gloria Macapagal-Arroyo and COMELEC Commissioner Virgilio Garcillano discussing the manipulation of the 2004 presidential election results, surfaced and caused a major political controversy. Both Houses of Congress initiated separate legislative inquiries into the matter, leading to the petitions filed in this case.

• Following the public emergence of the "Hello Garci" tapes, which allegedly contained conversations between President Arroyo and COMELEC Commissioner Garcillano about rigging the 2004 election results, the House of Representatives initiated an inquiry through its Committees on Public Information, Public Order and Safety, National Defense and Security, Information and Communications Technology, and Suffrage and Electoral Reforms.
• During the House inquiry, "original" tape recordings were submitted and eventually played in the House chambers. The House Committees decided to prepare reports based on these recordings and testimonies.
• Virgilio Garcillano filed G.R. No. 170338, seeking to prohibit the House Committees from using the tapes in their reports or for any other purpose, and to strike any reference to them from the records.
• Over two years later, Senator Panfilo Lacson revived the issue in a privilege speech, prompting the Senate Committee on National Defense and Security to initiate its own inquiry into the "Hello Garci" tapes and related wiretapping activities.
• Retired Court of Appeals Justices Santiago Ranada and Oswaldo Agcaoili filed G.R. No. 179275, seeking to prohibit the Senate from conducting its legislative inquiry, arguing it violated R.A. No. 4200 (Anti-Wiretapping Act) and Section 3, Article III of the Constitution.
• Maj. Lindsay Rex Sagge, an ISAFP member summoned by the Senate, intervened in G.R. No. 179275, alleging due process violations due to the lack of published Senate rules for inquiries and the absence of a stated legislative purpose.
• The two petitions were consolidated by the Supreme Court.

• Petitioner Garcillano (G.R. No. 170338) argued that the House Committees should be restrained from using the "illegally obtained" wiretapped recordings in their committee reports or for any other purpose, and that the recordings and references thereto should be stricken from the records of the inquiry.
• Petitioners Ranada and Agcaoili (G.R. No. 179275) argued that the Senate's intended legislative inquiry on the "Hello Garci" tapes violates R.A. No. 4200 (Anti-Wiretapping Act) and Section 3, Article III of the Constitution (right to privacy of communication).
• Petitioner-Intervenor Sagge (G.R. No. 179275) argued that his right to due process was violated because he was summoned to Senate hearings without being apprised of his rights through published Senate Rules of Procedure Governing Inquiries in Aid of Legislation for the 14th Congress, and without knowing the intended legislation. He also intervened as a taxpayer.

• Respondent House Committees (G.R. No. 170338) implicitly argued their authority to conduct the inquiry and use the tapes, having already played them and decided to prepare reports based thereon.
• Respondent Senate (G.R. No. 179275) and Respondents-Intervenors (Senators) argued that the Senate Rules of Procedure Governing Inquiries in Aid of Legislation had been published in newspapers in 1995 and 2006, were available in booklet form, and accessible on the Senate's website, thus satisfying the publication requirement.

• Whether petitioners Garcillano, Ranada, Agcaoili, and Sagge have legal standing (locus standi) to file their respective petitions.
• Whether the petition in G.R. No. 170338 (Garcillano's petition against the House Committees) has become moot and academic.
• Whether the Senate's legislative inquiry into the "Hello Garci" tapes is unconstitutional due to the alleged non-publication of its rules of procedure for such inquiries by the 14th Congress, as required by Section 21, Article VI of the Constitution.
• Whether the Senate inquiry violates R.A. No. 4200 and Section 3, Article III of the Constitution. (This issue was not extensively discussed due to the ruling on the publication requirement).

• The Supreme Court held that petitioners Garcillano, Ranada, Agcaoili, and Sagge all possess the requisite legal standing, applying a liberal approach due to the transcendental importance of the constitutional issues raised.
• The petition in G.R. No. 170338 (Garcillano) was dismissed for being moot and academic because the acts sought to be prohibited (playing of the tapes and submission of committee reports) had already been accomplished, and prohibition is a preventive, not a remedial, writ.
• The petition in G.R. No. 179275 (Ranada and Agcaoili) was granted. The Court ruled that the Senate could not conduct the legislative inquiry because its Rules of Procedure Governing Inquiries in Aid of Legislation were not duly published by the 14th Congress. Section 21, Article VI of the Constitution requires that such inquiries be conducted "in accordance with its duly published rules of procedure."
• The Court, citing Neri v. Senate Committee, reiterated that the Senate of each Congress is distinct, and its rules of procedure for legislative inquiries must be published by that specific Congress. Publication in previous Congresses (1995 and 2006) or availability in booklets or on the internet does not suffice for the 14th Congress. The recent publication (October 31, 2008) did not cure the infirmity for the inquiry subject of the petition.

• Locus Standi (Legal Standing) — Refers to a personal and substantial interest in a case such that the party has sustained or will sustain direct injury due to the challenged governmental act. The Court applied a liberal policy, recognizing standing for citizens and taxpayers when issues of transcendental importance or serious constitutional questions impacting public interest are involved. Garcillano had standing as the person alluded to in the tapes; Ranada, Agcaoili, and Sagge had standing as citizens, taxpayers, and due to the paramount constitutional issues.
• Moot and Academic Principle — A case becomes moot when its purpose has become stale or when no practical relief can be granted because the act sought to be enjoined has already been accomplished. Applied to Garcillano's petition (G.R. No. 170338) as the House had already played the tapes and submitted committee reports.
• Requirement of Duly Published Rules of Procedure for Legislative Inquiries (Section 21, Article VI, 1987 Constitution) — The Senate or House, or their committees, may conduct inquiries in aid of legislation only "in accordance with its duly published rules of procedure." This publication is mandatory and intended to satisfy due process. The Court held that "duly published" means publication by the current Congress, either in the Official Gazette or a newspaper of general circulation. Past publications or online availability do not suffice for a new Congress.
• Nature of the Senate as a Continuing Body vs. Non-Continuing for Conduct of Business — While the Senate as an institution is continuing, its conduct of business, including legislative investigations and its rules for such, terminates with the expiration of each Congress. Therefore, rules for inquiries must be republished by each new Congress unless the rules themselves explicitly provide for their continued effectivity until amended or repealed and are published accordingly.
• Due Process in Legislative Inquiries — Publication of rules of procedure is essential for due process, as it informs citizens of the procedures governing such inquiries and protects them from arbitrary action. The Court emphasized that it would be the height of injustice to punish or burden a citizen for transgressing a rule of which they had no notice.
• Prohibition as a Preventive Remedy — The writ of prohibition is a preventive remedy to restrain the doing of an act about to be done, and is not intended to provide a remedy for an act already accomplished. This was a basis for dismissing Garcillano's petition as moot.
• Electronic Commerce Act (R.A. No. 8792) and Publication — R.A. 8792, which gives legal recognition to electronic documents for evidentiary purposes, does not make the internet a valid medium for publishing laws, rules, and regulations to satisfy constitutional or statutory publication requirements for effectivity.

• "The phrase 'duly published rules of procedure' requires the Senate of every Congress to publish its rules of procedure governing inquiries in aid of legislation because every Senate is distinct from the one before it or after it." (Quoting OSG's explanation in Neri v. Senate Committee)
• "The language of Section 21, Article VI of the Constitution requiring that the inquiry be conducted in accordance with the duly published rules of procedure is categorical. It is incumbent upon the Senate to publish the rules for its legislative inquiries in each Congress or otherwise make the published rules clearly state that the same shall be effective in subsequent Congresses or until they are amended or repealed to sufficiently put public on notice."
• "The publication of the Rules of Procedure in the website of the Senate, or in pamphlet form available at the Senate, is not sufficient under the Tañada v. Tuvera ruling which requires publication either in the Official Gazette or in a newspaper of general circulation." (Quoting Justice Carpio's opinion in Neri v. Senate Committee)
• "R.A. 8792 considers an electronic data message or an electronic document as the functional equivalent of a written document only for evidentiary purposes. x x x It does not make the internet a medium for publishing laws, rules and regulations."

• Tolentino v. COMELEC — Cited for the definition of "legal standing" or locus standi.
• David v. Macapagal-Arroyo — Cited for the liberal policy on locus standi, allowing ordinary citizens, members of Congress, and civic organizations to prosecute actions involving constitutionality.
• Chavez v. Gonzales — Cited as an example of the Court's refusal to wield procedural barriers like locus standi as impediments to addressing serious legal questions impacting public interest.
• Francisco, Jr. v. The House of Representatives — Cited to support the standing of petitioners Ranada, Agcaoili, and Sagge based on their allegation that the Senate inquiry would involve expenditure of public funds and invocation of their rights as citizens and taxpayers.
• Neri v. Senate Committee on Accountability of Public Officers and Investigations — Heavily relied upon as controlling precedent for the requirement that the Senate of each Congress must publish its rules of procedure for inquiries in aid of legislation. The Court quoted extensively from both the main decision and Justice Carpio's Dissenting and Concurring Opinion in Neri.
• Arnault v. Nazareno — Referenced in Justice Carpio's opinion in Neri (and quoted in this case) regarding the non-continuing nature of the Senate under the 1935 Constitution, which was applied by analogy to the Senate under the 1987 Constitution concerning the publication of rules.
• Tañada v. Tuvera — Cited as the ruling that establishes the requirement of publication of laws (and by extension, rules of procedure for legislative inquiries that can affect citizens' rights) in the Official Gazette or a newspaper of general circulation for their effectivity, as a matter of due process.
• MCC Industrial Sales Corporation v. Ssangyong Corporation — Cited to explain that R.A. No. 8792 (Electronic Commerce Act) recognizes electronic documents as functional equivalents of written documents primarily for evidentiary purposes and does not establish the internet as a valid medium for the publication of laws or rules.

• 1987 Constitution, Article VI, Section 21 — This is the central provision, stating: "The Senate or the House of Representatives, or any of its respective committees may conduct inquiries in aid of legislation in accordance with its duly published rules of procedure. The rights of persons appearing in or affected by such inquiries shall be respected." Its mandatory publication requirement was the basis for granting the petition in G.R. No. 179275.
• 1987 Constitution, Article III, Section 3 — This provision on the inviolability of privacy of communication and correspondence was invoked by petitioners Ranada and Agcaoili, arguing the Senate inquiry would violate it by using illegally obtained wiretapped recordings. The Court did not rule definitively on this due to the procedural infirmity.
• Civil Code, Article 2 — This article, which states that "[l]aws shall take effect after 15 days following the completion of their publication either in the Official Gazette, or in a newspaper of general circulation in the Philippines," was cited in relation to what constitutes proper publication.
• Republic Act No. 4200 (Anti-Wiretapping Act) — Petitioners Ranada and Agcaoili argued the Senate inquiry would violate this Act. The Court did not rule on this issue due to the procedural grounds for granting the petition.
• Republic Act No. 8792 (Electronic Commerce Act of 2000) — Respondents invoked this Act to support their claim of valid publication through the internet. The Court rejected this, stating the Act primarily concerns the evidentiary value of electronic documents, not the mode of publishing laws or rules.
• Senate Rules, Rule XLIV, Sec. 123 (Unfinished Business) — Cited to show that all pending matters and proceedings terminate upon the expiration of one Congress, supporting the view that rules for inquiries do not automatically carry over.
• Senate Rules, Rule LI, Sec. 136 (Amendments to, or Revisions of, the Rules) — Cited to show the Senate's main rules acknowledge the new composition of the Senate after elections and the possibility of amendment/revision at the start of each session.
• Senate Rules, Rule LII, Sec. 137 (Date of Taking Effect) — The Court noted the difference in language between the Senate's main rules (which state they remain in force until amended/repealed) and the Rules of Procedure Governing Inquiries (which only state they take effect 7 days after newspaper publication), implying the latter do not automatically continue.

• Chief Justice Reynato S. Puno — The decision notes that C.J. Puno dissented, and that Justices Ynares-Santiago, Austria-Martinez, Carpio Morales, and Azcuna joined his dissenting opinion. The main text of the decision does not provide a summary of this dissent.
• Justice Ruben T. Reyes — The decision notes Justice Reyes had a concurring and dissenting opinion, but no summary of the dissenting part is provided in the main text.