The power to create provinces and cities, which inherently includes the power to create legislative districts, is vested exclusively in Congress and cannot be delegated to the ARMM Regional Assembly; therefore, any province or city created by the ARMM Regional Assembly under such delegated authority is void.

The 1987 Constitution apportioned two legislative districts for Maguindanao, with the first district including Cotabato City and eight municipalities. Maguindanao is part of the Autonomous Region in Muslim Mindanao (ARMM), but Cotabato City, despite being in its first legislative district, is not part of ARMM, having voted against inclusion. Republic Act No. 9054, amending the ARMM Organic Act, granted the ARMM Regional Assembly the power to create provinces. This grant of power and its subsequent exercise led to the legal disputes in this case.

• On August 28, 2006, the ARMM Regional Assembly enacted Muslim Mindanao Autonomy Act No. 201 (MMA Act 201), creating the Province of Shariff Kabunsuan from eight municipalities of Maguindanao's first legislative district.
• MMA Act 201 stipulated that "Except as may be provided by national law, the existing legislative district, which includes Cotabato City as a part thereof, shall remain."
• The creation of Shariff Kabunsuan was ratified in a plebiscite on October 29, 2006.
• Cotabato City, though part of Maguindanao's first legislative district as per the 1987 Constitution's Ordinance, is not part of ARMM but of Region XII.
• The Sangguniang Panlungsod of Cotabato City requested COMELEC to clarify its status following the creation of Shariff Kabunsuan.
• On March 6, 2007, COMELEC issued Resolution No. 07-0407, maintaining the status quo with Cotabato City as part of Shariff Kabunsuan in the First Legislative District of Maguindanao, pending Congressional action.
• On March 29, 2007, COMELEC issued Resolution No. 7845, stating that Maguindanao's first legislative district was now composed only of Cotabato City due to MMA Act 201.
• On May 10, 2007, COMELEC issued Resolution No. 7902, amending Resolution No. 07-0407, renaming the legislative district as "Shariff Kabunsuan Province with Cotabato City (formerly First District of Maguindanao with Cotabato City)." This resolution is the subject of the petitions.
• Bai Sandra Sema was a candidate for Representative of "Shariff Kabunsuan with Cotabato City" in the May 14, 2007 elections.
• Didagen P. Dilangalen was proclaimed representative of the legislative district of Shariff Kabunsuan Province with Cotabato City on June 1, 2007.

• Bai Sandra Sema (G.R. No. 177597) argued that Shariff Kabunsuan is entitled to one representative in Congress under the Constitution, and COMELEC Resolution No. 7902 is null for including Cotabato City in its legislative district, thereby usurping Congress's power to create or reapportion legislative districts.
• Sema later contended that Section 19, Article VI of RA 9054 (delegating power to ARMM to create provinces) is constitutional, and a province created by the ARMM Regional Assembly is ipso facto entitled to one representative in the House of Representatives without a separate national law creating its legislative district.
• Sema conceded that if taken literally, the grant in Section 19, Article VI of RA 9054 allowing ARMM to prescribe standards lower than RA 7160 for province creation contravenes the Constitution, proposing it be construed as prohibiting standards not complying with minimum RA 7160 criteria.
• Perfecto F. Marquez (G.R. No. 178628) argued that COMELEC acted ultra vires in issuing Resolution No. 7902, effectively depriving the voters of Cotabato City of a representative in the House of Representatives.

• The COMELEC (initially, through OSG) argued that certiorari was an improper remedy as Resolution No. 7902 was issued in its administrative capacity, and Sema's prayer for prohibition was moot due to Dilangalen's proclamation.
• The COMELEC later (in compliance with a Court order) joined Sema, contending that Section 5 (3), Article VI of the Constitution is "self-executing," entitling any new province created by ARMM to a representative ipso facto.
• Subsequently, the COMELEC (through OSG, joining Dilangalen) argued that Section 19, Article VI of RA 9054 is unconstitutional as it contravenes Article X, Sections 10 and 6 of the Constitution, and that the power to create provinces was withheld from autonomous regions under Section 20, Article X of the Constitution.
• The COMELEC (in its comment to G.R. No. 178628) maintained the validity of Resolution No. 7902 as a temporary measure pending Congressional enactment of an "appropriate law."
• Didagen P. Dilangalen argued that Sema was estopped from questioning Resolution No. 7902 as her certificate of candidacy indicated she was running for "Shariff Kabunsuan including Cotabato City."
• Dilangalen contended that Resolution No. 7902 was constitutional as it merely renamed Maguindanao's first legislative district, not apportioned or reapportioned districts, a power exclusive to Congress.
• Dilangalen argued that the "province" in Section 5 (3), Article VI of the Constitution refers to one created by Congress, and Section 3, Article IV of RA 9054 withheld from ARMM the power to enact measures on national elections, including legislative apportionment.
• Dilangalen asserted that Cotabato City, with a population less than 250,000, is not entitled to its own representative.

• Whether the writs of Certiorari, Prohibition, and Mandamus are proper to test the constitutionality of COMELEC Resolution No. 7902.
• Whether the proclamation of respondent Dilangalen mooted the petition in G.R. No. 177597.
• Whether Section 19, Article VI of RA 9054, delegating to the ARMM Regional Assembly the power to create provinces, cities, municipalities, and barangays, is constitutional.
• If Section 19, Article VI of RA 9054 is constitutional, whether a province created by the ARMM Regional Assembly under this provision is entitled to one representative in the House of Representatives without a national law creating a legislative district for such province.
• Whether COMELEC Resolution No. 7902 is valid for maintaining the status quo in the first legislative district of Maguindanao (as "Shariff Kabunsuan Province with Cotabato City") despite the creation of the Province of Shariff Kabunsuan.

• The writ of Prohibition is an appropriate remedy to test the constitutionality of election laws, rules, and regulations like COMELEC Resolution No. 7902.
• Respondent Dilangalen's proclamation did not moot the petition as the case involves the validity of COMELEC Resolution No. 7902, MMA Act 201, and Section 19, Article VI of RA 9054, which have broader implications.
• Section 19, Article VI of RA 9054 is unconstitutional insofar as it grants the ARMM Regional Assembly the power to create provinces and cities. The power to create provinces or cities inherently involves the power to create legislative districts, as each province and each city with at least 250,000 population is constitutionally entitled to at least one representative. This power to create or reapportion legislative districts is vested exclusively in Congress by Section 5, Article VI of the Constitution and cannot be delegated.
• Consequently, Muslim Mindanao Autonomy Act No. 201, creating the Province of Shariff Kabunsuan, enacted by the ARMM Regional Assembly, is void.
• A province created by the ARMM Regional Assembly is not automatically entitled to a representative in the House of Representatives. Only an Act of Congress can create a legislative district, either directly or as a consequence of creating a province by national law.
• COMELEC Resolution No. 7902, which preserved the geographic and legislative district of the First District of Maguindanao (including Cotabato City) under a new name, is valid as it complies with the Constitution by not recognizing a new legislative district for an invalidly created province and by maintaining the existing district as defined by Congress and the Constitution's Ordinance.

• Exclusive Power of Congress to Create and Reapportion Legislative Districts — This doctrine states that the authority to create new legislative districts or alter existing ones is vested solely in the National Legislature (Congress). It was applied to invalidate Section 19, Article VI of RA 9054 (insofar as it allowed ARMM to create provinces and cities) because the creation of a province or a city (with 250,000+ population) constitutionally necessitates the creation of a legislative district, a power non-delegable by Congress.
• Creation of a Province or City Inherently Involves Power to Create a Legislative District — The Constitution mandates that each province, and each city with a population of at least 250,000, shall have at least one representative in the House of Representatives. This means the act of creating such entities inherently includes the power to create a legislative district for them. This doctrine was used to demonstrate that since the ARMM Regional Assembly cannot create legislative districts, it cannot validly create provinces or cities that would automatically require such districts.
• Non-delegation of Legislative Power (for specific constitutional functions) — While Congress has plenary legislative power and can delegate some functions, powers textually committed by the Constitution exclusively to Congress (like creating legislative districts for the House of Representatives) cannot be delegated. This was applied to argue that Congress could not delegate to the ARMM Regional Assembly the power to create provinces/cities if such creation would result in new congressional districts, as this would effectively allow an inferior legislature to alter the composition of Congress.
• Supremacy of the Constitution — All laws, including organic acts, must conform to the Constitution. Any provision of a statute or organic act that contravenes the Constitution is void. This principle was applied to declare Section 19, Article VI of RA 9054 unconstitutional and MMA Act 201 void because they violated the constitutional provision vesting the power to create legislative districts exclusively in Congress.
• Writ of Prohibition as a Remedy for Unconstitutional Acts — The writ of prohibition is a proper legal remedy to challenge the constitutionality of election laws, rules, and regulations issued by bodies like the COMELEC when they act without or in excess of jurisdiction or with grave abuse of discretion. This doctrine affirmed the appropriateness of the remedy sought by the petitioners to question COMELEC Resolution No. 7902.
• Limitations on Legislative Powers of Autonomous Regions — The legislative powers of autonomous regions, as provided in their organic acts, are exercised "[w]ithin its territorial jurisdiction and subject to the provisions of this Constitution and national laws" (Article X, Section 20, Constitution). This was applied to show that the ARMM Regional Assembly cannot enact laws creating national offices (like a district representative) or altering the composition of a national body (Congress).

• "Clearly, a province cannot be created without a legislative district because it will violate Section 5 (3), Article VI of the Constitution as well as Section 3 of the Ordinance appended to the Constitution... Thus, the power to create a province or city inherently involves the power to create a legislative district."
• "Under the present Constitution, as well as in past Constitutions, the power to increase the allowable membership in the House of Representatives, and to reapportion legislative districts, is vested exclusively in Congress."
• "It would be anomalous for regional or local legislative bodies to create or reapportion legislative districts for a national legislature like Congress. An inferior legislative body, created by a superior legislative body, cannot change the membership of the superior legislative body."
• "Only Congress can create provinces and cities because the creation of provinces and cities necessarily includes the creation of legislative districts, a power only Congress can exercise under Section 5, Article VI of the Constitution and Section 3 of the Ordinance appended to the Constitution."

• Felwa v. Salas (124 Phil. 1226 (1966)) — Cited by petitioner Sema for the proposition that when a province is created by statute, the corresponding representative district comes into existence by operation of the Constitution. The Court distinguished this, stating Felwa involved provinces created by a national law enacted by Congress itself, unlike Shariff Kabunsuan which was created by a regional law. The Court clarified that only an act of Congress can trigger the creation of a legislative district by operation of the Constitution.
• Montejo v. COMELEC (312 Phil. 492 (1995)) — Cited to support the principle that the "power of redistricting x x x is traditionally regarded as part of the power (of Congress) to make laws," and thus is vested exclusively in Congress.

• Constitution, Article VI, Section 5(1), (3), and (4) — These sections detail the composition of the House of Representatives, the requirement for each province and certain cities to have at least one representative, the standards for legislative districts, and the exclusive power of Congress to reapportion legislative districts. These were central to the ruling that only Congress can create legislative districts.
• Constitution, Article X, Section 10 — This section provides that no province, city, municipality, or barangay may be created except in accordance with criteria in the local government code and subject to a plebiscite. While relevant to LGU creation, it was held not to override Congress's exclusive power over legislative districts.
• Constitution, Article X, Section 20 — This section enumerates the legislative powers of autonomous regions, which are to be exercised "within its territorial jurisdiction and subject to the provisions of this Constitution and national laws." This was used to argue that ARMM's powers do not extend to creating national offices or altering Congress.
• Ordinance Appended to the 1987 Constitution, Section 3 — This section states that any province thereafter created shall be entitled to at least one Member in the House of Representatives. The Court interpreted "province that may hereafter be created" to mean a province created by Congress itself.
• Republic Act No. 9054 (ARMM Organic Act), Article VI, Section 19 — This provision, granting the ARMM Regional Assembly power to create provinces and cities, was declared unconstitutional insofar as it allows the creation of provinces and cities, as this power is tied to the creation of legislative districts.
• Republic Act No. 9054 (ARMM Organic Act), Article IV, Section 3(k) — This provision states that the Regional Assembly may exercise legislative power except on "National elections." This was cited to support the argument that ARMM cannot create legislative districts whose representatives are elected in national elections.
• Muslim Mindanao Autonomy Act No. 201 — The act passed by the ARMM Regional Assembly creating the Province of Shariff Kabunsuan. This Act was declared void as a consequence of the unconstitutionality of the enabling provision in RA 9054.
• Republic Act No. 7160 (Local Government Code), Section 461 — This section provides the criteria for the creation of a province (income, territory/population). The Court noted that ARMM-created provinces would still need to meet these criteria, but this did not save the ARMM's power to create them due to the legislative district issue.
• COMELEC Resolution No. 7902 — The challenged resolution which renamed the first legislative district of Maguindanao to include Shariff Kabunsuan and Cotabato City. It was declared valid as it merely maintained the existing legislative district.

• Justice Dante O. Tinga (Dissenting and Concurring) — Justice Tinga agreed with the majority that the petitions should be denied (concurring in the result) but dissented from the reasoning that the ARMM Regional Assembly cannot be delegated the power by Congress to create provinces. He argued that Congress can delegate the power to create provinces to the Regional Assembly, and such delegation is in furtherance of local autonomy. However, he concurred that an ARMM-created province cannot automatically acquire its own legislative district because the power to increase the composition of the House of Representatives is non-delegable and textually committed by the Constitution solely to Congress. Thus, while the creation of the province by ARMM could be valid, it would not automatically result in a new legislative district without a law passed by Congress. He criticized the majority for dealing a "severe blow to the cause of local autonomy" by invalidating the ARMM's power to create provinces.