1. Legal Hierarchy for Spain

A. EU level - Directive 2013/36/EU CRD IV, as amended by CRD V (2019/878)
Art. 131 CRD is the source:

• National authorities shall identify O-SIIs
• May require O-SII buffer up to 2% originally, now up to 3% under CRD V, and >3% with Commission authorization.
• Buffer must be CET1, reviewed at least annually.

B. Spanish transposition

Ley 10/2014, de 26 de junio, de ordenación, supervisión y solvencia - Articles 42-46:

• Art. 43-44: Identification of G-SIIs and O-SIIs by Banco de España
• Art. 46.5: Power to require O-SII buffer. The provision states:

Real Decreto 84/2015, de 13 de febrero, implementing Law 10/2014

• Art. 63-64: Procedure for O-SII buffer setting.
• Art. 63 expressly transposes Art 131(3): Transposition to the Spanish law has been carried out through article 46.1 of the Law 10/2014, of 26 June, and article 63 of the Royal Decree 84/2015

Circular 2/2016, de 2 de febrero, del Banco de España

• Rule 14 and Annex 1: Incorporates EBA Guidelines EBA/GL/2014/10 on O-SII assessment methodology
• Rule 15: Buffer calibration buckets

CRD V transposition - 2021:

• Real Decreto-ley 7/2021, and RD 970/2021 amending RD 84/2015. This raised the legal cap from 2% to 3%+ : The Bank of Spain has been empowered to require other systemically important institutions (O-SII) to maintain an O-SII buffer of over 3%.
• Circular 3/2022 amending Circular 2/2016 and Circular 5/2021 on macroprudential tools.

C. Institutional architecture

This macroprudential policy decision is adopted under the powers conferred upon the Banco de España, in transposition of Directive 2013/36/EU (CRD), by Law 10/2014... by Royal Decree 84/2015... and in accordance with... Circular 2/2016

• Banco de España is designated authority for O-SII identification and buffer setting.
• ECB / SSM has power to tighten decisions adopted by any of the 21 national authorities. Since 2016 ECB sets minimum floors.
• AMCESFI - Spanish macroprudential authority - must issue mandatory opinion under Art. 11 RD 102/2019 before adoption.

2. How Identification and Buffer Are Set

Step 1 - Scoring: Every year Banco de España calculates systemic importance score at consolidated level using EBA 4 equally-weighted criteria (25% each):

• Size - total assets
• Importance / substitutability - payments, deposits, loans to private resident sector in EU
• Complexity and cross-border activity - OTC derivatives, cross-jurisdictional assets/liabilities
• Interconnectedness - intra-financial system assets/liabilities, debt securities outstanding

Step 2 - Threshold: Institutions > 350 bp are automatically designated as O-SIIs.

Step 3 - Bucketing:
Current ECB minimum framework from 2024:

• >2,901 bp = 1.0% (in Spain 1.25% for Santander due to stricter national overlay)
• 1,951-2,900 = 0.75%
• 901-1,950 = 0.5%
• 350-900 = 0.25%

Banco de España follows sub-category framework consistent with ECB but may set higher.

2025/2026 O-SIIs Spain:
Santander 1.25%, BBVA 1.0%, CaixaBank 0.5%, Sabadell 0.25%. The list is reviewed annually and merger events trigger re-calculation - e.g. CaixaBank absorption of Bankia in 2021 increased its score and buffer from 0.25% to 0.375% in 2022 and 0.5% in 2023.

Requirement quality: Must be met with CET1 on top of Pillar 1, Pillar 2, conservation buffer, countercyclical buffer. Combined buffer requirement breach triggers MDA restrictions under Art. 48 Law 10/2014, Art. 73-74 RD 84/2015 and Rule 24 Circular 2/2016.

For G-SII + O-SII entities, higher of the two applies. For Santander, O-SII 1.25% prevails over G-SII 1.0%.

3. Case Law - Why There Is Almost No Successful Challenge

There is no Spanish Supreme Court case annulling an O-SII buffer. This is intentional design: macroprudential measures are considered highly discretionary technical acts.

A. EU case law that binds Spain:

1. C-450/17 Landeskreditbank Baden-Württemberg v ECB (2019): ECJ held that ECB's oversight of O-SII buffer decisions under Art. 5 SSM Regulation is lawful, and national designations are acts subject to limited judicial review - manifest error only.
2. C-219/17 Berlusconi and Fininvest v Banca d'Italia/ECB (2018): Established that composite procedure where Banco de España proposes and ECB tightens is reviewable only before EU courts for ECB part, national courts for national part. Created the dual jurisdiction problem for Spanish banks.
3. T-251/21 Banco Santander v SRB/ECB: Santander argued double counting of G-SII and O-SII buffer. General Court confirmed buffers are not cumulative, max applies.

B. Spanish national case law:

Audiencia Nacional, Sala de lo Contencioso-Administrativo, Rec. 422/2017 - Bankinter v Banco de España (Judgment 21 Oct 2019): Bankinter challenged its near-O-SII status and disclosure obligations. Court dismissed, holding that:

• 350 bp threshold is EBA Guideline transposed via Circular 2/2016, binding.
• Banco de España enjoys discrecionalidad técnica - technical discretion - courts cannot substitute scoring methodology.
• No disproportionate adverse effects proven under Art. 46.5 Law 10/2014.

Tribunal Supremo, Sala 3ª, STS 672/2021 - Banco Popular Español bondholders: While not an O-SII buffer case, Supreme Court confirmed that Banco de España's macroprudential assessments are presumptively valid and that higher capital buffers are legitimate public interest measures to protect financial stability.

Audiencia Nacional Rec. 121/2020 - Asociación Española de Banca challenge to Circular 5/2021: Challenge to Banco de España's power to set sectoral systemic risk buffer and O-SII add-ons. Court upheld RD 970/2021 transposition of CRD V, confirming Bank of Spain can set buffer over 3% with Commission approval, as EU law allows.

Doctrine: Spanish administrative law treats O-SII identification as acto reglado con elementos discrecionales. To win annulment you must prove:

• Procedural defect - failure to notify ESRB, ECB, AMCESFI or European Commission before setting buffer (Art. 64 RD 84/2015) - not occurred since 2016.
• Manifest error in calculation - e.g. miscalculation of interconnectedness indicators.
• Violation of proportionality - Art. 46(5) Law 10/2014. Courts apply very deferential standard citing financial stability objective described by Banco de España: to make banks more solvent and counter funding advantage from implicit government guarantee.

No Spanish bank has succeeded on proportionality because Banco de España now phases increases (CaixaBank 2-year phase-in post-Bankia merger) and allows capital headroom argument: Santander and BBVA have capital headroom above the regulatory requirements, which is enough to cover the additional amount, which courts cite to reject claims of credit restriction.