The Senate may not validly elect as members of the Senate Electoral Tribunal Senators who have not been nominated by the political parties specified in Article VI, Section 11 of the Constitution; the party having the largest number of votes in the Senate is entitled to nominate three members, and the party having the second largest number of votes has the exclusive right to nominate the other three Senator-members. Any nomination for these constitutionally allocated party slots made by an entity other than the designated political party is null and void.

The dispute originated from the organization of the Senate Electoral Tribunal after the 1955 general elections. At that time, the Senate was overwhelmingly dominated by the Nacionalista Party, which had 23 Senators, while the Citizens Party, represented solely by Senator Lorenzo M. Tañada, was the party with the second largest number of votes. The constitutional provision for the Senate Electoral Tribunal requires six Senators as members: three to be nominated by the party with the largest number of votes and three by the party with the second largest number of votes. The conflict centered on how these nominations, particularly for the minority slots, should proceed given this significant disparity in party representation.

• Petitioner Lorenzo M. Tañada was a Senator and President of the Citizens Party. Petitioner Diosdado Macapagal, a Liberal Party candidate for the Senate in the 1955 elections, had an election protest pending before the Senate Electoral Tribunal.
• In February 1956, the Senate comprised 23 Nacionalista Party (NP) members and one Citizens Party (CP) member, Senator Tañada.
• On February 22, 1956, during the Senate session to organize the Senate Electoral Tribunal, Senator Cipriano Primicias (NP Floor Leader) nominated three NP Senators (Laurel, Lopez, and Primicias), who were subsequently chosen by the Senate.
• Senator Tañada, on behalf of the Citizens Party (acknowledged as the party with the second largest number of votes), nominated himself as a member of the Tribunal, and he was chosen.
• Senator Primicias then, purportedly on behalf of the Senate Committee on Rules (not the Citizens Party), nominated Senators Mariano J. Cuenco and Francisco A. Delgado (both NP) to fill the remaining two Senatorial seats in the Tribunal.
• Senators Tañada and Sumulong formally objected to these latter nominations, arguing they were unconstitutional as the right to nominate these members belonged exclusively to the Citizens Party.
• Despite these objections, the Senate proceeded to choose Senators Cuenco and Delgado as members of the Tribunal.
• Consequently, staff members (technical assistants and private secretaries) were appointed for Senators Cuenco and Delgado in their capacities as purported members of the Senate Electoral Tribunal.

• The election of Senators Cuenco and Delgado to the Senate Electoral Tribunal was unconstitutional and void because they were not nominated by the Citizens Party, which, as the party with the second largest number of votes in the Senate, had the exclusive right to nominate three members under Article VI, Section 11 of the Constitution.
• The Nacionalista Party, through the Committee on Rules, effectively usurped the Citizens Party's nominating power, thereby violating the constitutional design for a balanced and impartial Tribunal.
• The resulting composition of the Tribunal, with five Nacionalista Party members and only one Citizens Party member, undermined the constitutional rights of petitioner Macapagal to have his election protest decided by a properly constituted Tribunal.
• The appointments of staff for Senators Cuenco and Delgado were consequently illegal as their principals were not lawful members of the Tribunal.

• The Supreme Court lacks jurisdiction to review the Senate's choice of Electoral Tribunal members, as this is a political question solely within the Senate's purview.
• The petition states no cause of action because Senator Tañada, by nominating only himself, either waived his party's right to nominate more members or exhausted it, and is now estopped from challenging the subsequent nominations.
• The proper remedy for the petitioners is an appeal to public opinion, not a judicial action.
• The constitutional requirement for the Electoral Tribunal to have nine members (including six Senators) is mandatory, and the Senate acted to fulfill this numerical composition after Senator Tañada nominated only one person.
• Senators Cuenco and Delgado are de jure members of the Tribunal, and their staff appointments are therefore valid.

• Whether the Supreme Court has jurisdiction to review the acts of the Senate in choosing members of the Senate Electoral Tribunal, or if this is a non-justiciable political question.
• Whether the election of Senators Cuenco and Delgado as members of the Senate Electoral Tribunal, nominated by the Senate Committee on Rules (representing the majority party) instead of by the Citizens Party (the party with the second largest number of votes), violated Article VI, Section 11 of the Constitution.
• Whether Senator Tañada, on behalf of the Citizens Party, waived the right to nominate additional members or is estopped from questioning the validity of the nominations of Senators Cuenco and Delgado.
• Whether the appointments of the co-respondent staff members for Senators Cuenco and Delgado are valid.

• The Supreme Court has jurisdiction over the petition. The issue presented is not a political question but one of constitutional interpretation – specifically, whether the Senate adhered to the mandatory procedures outlined in the Constitution for selecting members of the Senate Electoral Tribunal. The Court has the duty to determine if constitutional provisions have been violated.
• The election of Senators Cuenco and Delgado to the Senate Electoral Tribunal is null and void ab initio. Article VI, Section 11 of the Constitution explicitly requires that three of the six Senator-members be chosen upon nomination by the party having the largest number of votes, and the other three upon nomination by the party having the second largest number of votes. The Citizens Party, as the party with the second largest number of votes, possessed the exclusive constitutional right to nominate these three members. The nomination of Senators Cuenco and Delgado by the Committee on Rules (effectively by the Nacionalista Party) contravened this clear constitutional mandate. The intent behind this provision is to ensure a balance of power and impartiality within the Tribunal, which would be nullified if the majority party could fill slots designated for the minority party.
• Senator Tañada did not waive his party's constitutional right to nominate the remaining two members, nor is he estopped from challenging the unconstitutional nominations. The right to nominate is vested by the Constitution in the political party to uphold public policy concerning the Tribunal's integrity and cannot be waived in a manner that subverts the constitutional scheme. Estoppel is inapplicable as Senator Tañada consistently objected, and the issue involves a question of law regarding constitutional interpretation, not merely facts of which the Senate was unaware.
• Regarding the staff appointments of respondents Alfredo Cruz, Catalina Cayetano, Manuel Serapio, and Placido Reyes, the Court did not declare them null and void, noting they were appointed by the Tribunal's Chairman. The Court indicated that the Tribunal itself should take appropriate measures concerning these appointments in light of the decision.
• The Court declared that Senators Cuenco and Delgado were not duly elected members of the Senate Electoral Tribunal and enjoined them from acting as such.

• Judicial Supremacy / Power of Judicial Review — The authority of the judiciary to interpret the Constitution and to determine whether the acts of other branches of government are in conformity with it. Applied here to assert the Court's power to review the Senate's compliance with constitutional provisions for selecting Electoral Tribunal members, as the Tribunal is a constitutional body distinct from the Senate itself.
• Political Question Doctrine — The doctrine holding that certain questions are to be decided by the political branches of government (executive or legislative) and are not subject to judicial review because they involve policy rather than legality. The Court found this doctrine inapplicable because the case involved the interpretation of a specific constitutional mandate regarding the composition of the Electoral Tribunal, not a matter of legislative or executive discretion or wisdom.
• Constitutional Construction (Mandatory vs. Directory Provisions; Spirit over Letter) — The principle that constitutional provisions are generally presumed mandatory unless a directory interpretation is clearly intended. The Court held that the procedure for nomination to the Electoral Tribunals by specified political parties, as outlined in Article VI, Section 11, is mandatory because it is essential to the fundamental purpose of the Tribunal – ensuring impartiality and a balance of power. The spirit and purpose of the provision (to prevent partisan control) guided its interpretation.
• Separation of Powers — The constitutional principle distributing governmental powers among the legislative, executive, and judicial branches. The Court clarified that its review of the Senate's action was not an encroachment on the Senate's legislative powers, as the Electoral Tribunal is an independent constitutional body, and the issue was the legality of the Senate's compliance with the Constitution in forming this body.
• Waiver of Constitutional Rights — The principle that while individuals can waive certain personal constitutional rights, rights imbued with public policy considerations, such as those structuring governmental bodies for impartiality, cannot be waived if it undermines the constitutional design. The Court held that the Citizens Party's right to nominate was a matter of public policy essential to the Tribunal's integrity and could not be waived by Senator Tañada to legitimize an unconstitutional process.
• Estoppel — A legal bar preventing a party from denying or alleging a certain fact owing to that party's previous conduct, allegation, or denial. The Court ruled estoppel did not apply to Senator Tañada as he consistently objected to the nominations, and the issue was one of constitutional law, not a misrepresentation of fact upon which the Senate relied to its detriment.
• Statutory Construction (Ratio Legis / Legislative Intent) — The Court extensively analyzed the historical background and deliberations of the Constitutional Convention regarding the Electoral Tribunals. This revealed the framers' clear intent to create an independent, impartial body for adjudicating election contests by ensuring equal representation from the majority and minority parties, with Supreme Court Justices providing a neutral balancing force. This underlying purpose was crucial in interpreting the nomination requirements as mandatory.

• "The courts are called upon to say, on the one hand, by whom certain powers shall be exercised, and on the other hand, to determine whether the powers thus possessed have been validly exercised. In performing the latter function, they do not encroach upon the powers of a coordinate branch of the government, since the determination of the validity of an act is not the same thing as the performance of the act."
• "In short, the term 'political question' connotes, in legal parlance, what it means in ordinary parlance, namely, a question of policy... It is concerned with issues dependent upon the wisdom, not legality, of a particular measure."
• "The main objective of the framers of our Constitution in providing for the establishment... of one Electoral Tribunal for each House of Congress, was to insure the exercise of judicial impartiality in the disposition of election contests affecting members of the lawmaking body."
• "With the absolute majority thereby attained by the majority party in said Tribunal, the philosophy underlying the same would be entirely upset. The equilibrium between the political parties therein would be destroyed. What is worst, the decisive moderating role of the Justices of the Supreme Court would be wiped out... which is precisely what the fathers of our Constitution earnestly strove to forestall."
• "The procedure prescribed in said provision [Art. VI, Sec. 11] for the selection of members of the Electoral Tribunals is vital to the role they are called upon to play. It constitutes the essence of said Tribunals. Hence, compliance with said procedure is mandatory, and acts performed in violation thereof are null and void."

• Angara vs. Electoral Commission (63 Phil., 139) — Heavily relied upon to establish the Supreme Court's power of judicial review, the independence of Electoral Commissions/Tribunals from the legislature, and the framers' intent to create an impartial body for election contests through balanced party representation and judicial participation.
• Alejandrino vs. Quezon (46 Phil., 83) and Vera vs. Avelino (77 Phil., 192) — Distinguished by the Court as these cases involved direct actions against the Senate concerning its internal legislative functions, unlike the present case which concerned the constitutional composition of the separate Senate Electoral Tribunal.
• Suanes vs. Chief Accountant (81 Phil., 818) — Cited to support the view that the Electoral Tribunal is not part of Congress and that the Court had previously exercised jurisdiction over matters concerning the Tribunal. Also referenced regarding the Tribunal's internal control over its personnel.
• Mabanag vs. Lopez Vito (78 Phil., 1) — Distinguished as dealing with a political question regarding the internal process of the Senate for a constitutional amendment, whereas the current case involved adherence to a specific constitutional procedure for forming the Electoral Tribunal.
• Avelino vs. Cuenco (83 Phil., 17) — Mentioned as a case where the Court did intervene to determine a matter related to Senate proceedings (quorum), thereby limiting the scope of the political question doctrine.
• Cabili vs. Francisco (88 Phil., 654) — Distinguished because it concerned the Senate's reorganization of its representation in the Commission on Appointments, a matter involving political alignments and deemed a political question, unlike the present case which involved a clear constitutional mandate for party nomination to the Electoral Tribunal.

• Article VI, Section 11 of the Philippine Constitution — The central provision analyzed, which mandates the composition of Electoral Tribunals for each House of Congress. It specifies nine Members: three Supreme Court Justices and six Members of the respective House, with three to be chosen upon nomination of the party having the largest number of votes and three upon nomination of the party having the second largest number of votes. The Court interpreted the party nomination process as mandatory and exclusive to the designated parties.
• Rule 68, sec. 68 [a], Rules of Court (on Estoppel) — Referenced to explain why the doctrine of estoppel was not applicable to petitioner Tañada, as he did not mislead the Senate and the issue was primarily one of constitutional law.

• Paras, C.J. — Argued that the constitutional requirement for the Electoral Tribunal to be composed of nine members is the paramount consideration. He cited a 1939 opinion by Secretary of Justice Jose A. Santos, rendered when the National Assembly was composed of only one party, suggesting that the single party could nominate all six legislative members to ensure the Tribunal's full complement. Chief Justice Paras believed that the subsequent 1940 constitutional amendments, which retained the nine-member requirement with awareness of potential one-party dominance, supported this interpretation. Thus, if the minority party fails to nominate its full share, the Senate is justified in electing members to complete the nine-member composition, with party affiliation not being an absolute requirement for the nominees.
• Labrador, J. — Contended that all provisions of Article VI, Section 11 are mandatory, including both the nine-member composition and the method of nomination. He proposed that Senator Tañada's refusal to nominate two additional members should be construed as a waiver of a constitutional privilege. This waiver then allows the Senate, which has the power to "choose" the members, to elect the remaining two senators to fulfill the mandatory nine-member composition, thereby reconciling the different parts of the constitutional provision. He believed the Senate's action was not clearly violative of the Constitution and thus the Court should not intervene.