Challenge to IS 2025 Models: What Companies Can Do Now

Key data

The declaration models for Corporate Income Tax for fiscal year 2025 are being challenged in court. DISA Corporación Petrolífera, SA has filed administrative contentious proceedings 1002/2026 before the National Court (Administrative Contentious Chamber, Second Section) against the Order HAC/529/2026, the regulation that approves these models.

The Resolution of September 21, 2026, from the General Technical Secretariat, publishes the mandatory summons so that any interested party may appear in the proceedings. This is not a minor procedural step: the outcome of the challenge could have direct consequences on the validity or content of the forms that all companies must use to declare IS for 2025.

What does this regulation establish?

The resolution published on September 29, 2026 fulfills a specific procedural function: to publicly notify that administrative contentious proceedings are underway and to open the deadline for interested third parties to join the proceedings.

The key elements of the proceedings are as follows:

• Challenged regulation: Order HAC/529/2026, which approves the declaration models for Corporate Income Tax and Non-Resident Income Tax (IRNR) corresponding to the tax periods of 2025.
• Claimant: DISA Corporación Petrolífera, SA, a major company in the oil sector.
• Court: National Court, Administrative Contentious Chamber, Second Section.
• Case number: 1002/2026.
• Deadline to appear: 9 days from publication of the resolution in the BOE (29/09/2026).
• Standing to appear: any taxpayer or entity affected by Order HAC/529/2026, not just the original claimant.

Although the challenge is initiated by a company in the oil sector, the challenge concerns a regulation of general scope: IS models affect virtually all Spanish companies. If the National Court were to uphold the challenge in whole or in part, it could declare null or modify the models that companies must use for their declaration for fiscal year 2025.

Economic and operational impact

The immediate impact of this resolution is not economic in itself, but rather procedural and strategic. However, the business implications are relevant in two respects:

• Uncertainty about current models: While the challenge is pending, there is legal uncertainty about whether the models approved by Order HAC/529/2026 are fully valid. Companies must continue using the current models to comply with their obligations, but it is advisable to monitor the progress of the proceedings.
• Possible nullity or modification of models: If the National Court upholds the challenge, it could require the Administration to approve new models or correct existing ones. This could generate rectification or supplementary filing obligations for companies that have already filed their declaration.
• Cost of appearing: Companies that decide to appear in the proceedings must bear the costs of legal representation before the National Court, which involves the intervention of a lawyer and a court representative.

In operational terms, the 9-day deadline from September 29, 2026 is very tight. Companies that believe their interests may be affected must act quickly to not miss the opportunity to appear.

Who does it affect?

• All commercial companies required to file Corporate Income Tax for fiscal year 2025.
• Non-resident entities subject to Non-Resident Income Tax (IRNR) with or without permanent establishment, for tax periods of 2025.
• Tax groups that are taxed under a consolidated tax regime.
• Companies in the oil and energy sector with special exposure, given the profile of the claimant.
• Tax advisors and law firms that manage IS 2025 declarations for their clients.
• CFOs and financial directors of any company that must file IS 2025 and want to monitor regulatory risk.

Practical example

A medium-sized company in the energy sector, required to file IS for fiscal year 2025, discovers that Order HAC/529/2026 includes a field or requirement in the declaration model that it considers contrary to law or that generates a disproportionate burden.

When the Resolution of September 21, 2026 is published, this company has a deadline of 9 days (counted from 29/09/2026) to appear in administrative contentious proceedings 1002/2026 before the National Court. If it does not do so within that deadline, it loses the opportunity to be a party to the proceedings and to defend its interests directly in the litigation, although it could still be affected by the judgment rendered.

If the National Court were to uphold the challenge and declare certain aspects of the model null, this company could be required to file a supplementary or amended declaration, with the administrative and advisory costs that this entails.

What should companies do now?

1. Assess whether Order HAC/529/2026 causes any specific harm to your company. If any aspect of the 2025 IS model negatively affects your company, now is the time to act. Consult with your tax advisor if there is a basis for joining the challenge.
2. Act before the 9-day deadline expires. The deadline to appear in proceedings 1002/2026 runs from September 29, 2026. If your company wants to appear, it must initiate proceedings immediately with a lawyer and court representative authorized before the National Court.
3. Continue filing IS 2025 with the current models. The existence of the challenge does not suspend the obligation to file. Until there is a court ruling, the models approved by Order HAC/529/2026 remain official.
4. Monitor the progress of the proceedings. The National Court's judgment may take months or years. Set up an alert system to learn of the outcome and act if any aspect of the model is declared null.
5. Document any harm resulting from the current model. If the judgment were favorable to the claimant, having documentation of the harm suffered will facilitate possible claims or subsequent rectifications.

Official source

View complete regulation in official source

Disclaimer: This article is for informational purposes only and does not constitute legal advice. For specific decisions, consult a qualified professional. Source: https://www.boe.es/diario_boe/txt.php?id=BOE-A-2026-20243