Key data
| Challenged regulation | Order HAC/529/2026, of May 7, which approves the declaration models for IS and IRNR for fiscal year 2025 |
|---|---|
| Legal challenge | Administrative litigation 998/2026, filed by Inverama, SL |
| Judicial body | National Court, Administrative Litigation Chamber, Second Section |
| Publication of summons | September 29, 2026 (BOE-A-2026-20244) |
| Deadline to intervene | 9 business days from publication in the BOE |
| Entry into force of effect | Not specified (pending judicial resolution) |
| Affected parties | All corporations and entities required to file IS for fiscal year 2025 |
| Category | Tax Updates |
| Fiscal year | 2025 |
The official models with which thousands of Spanish corporations will file their Corporate Income Tax declaration for fiscal year 2025 are being challenged before the National Court. The company Inverama, SL has filed the administrative litigation 998/2026 against the Order HAC/529/2026, of May 7, which is precisely the regulation that approves said declaration models.
On September 29, 2026, the General Technical Secretariat of the Ministry of Finance published in the BOE the official summons, opening a period of 9 business days for any person or entity with legitimate interest to intervene in the proceedings. After that deadline, it is no longer possible to join the proceedings as a party.
What does this regulation establish?
The resolution published on September 29, 2026 does not modify any tax obligation directly. What it does is publicly notify that there is an active legal challenge against the official IS 2025 models and opens the deadline for interested third parties to join the proceedings.
The challenged regulation, the Order HAC/529/2026, is the one that each year approves the forms and models that corporations must use to file their Corporate Income Tax declaration. In this case, it covers the tax periods of fiscal year 2025 and also affects the Non-Resident Income Tax (IRNR).
The challenge has been filed by Inverama, SL before the Second Section of the Administrative Litigation Chamber of the National Court. Until the court rules, the models remain valid and filing obligations are maintained. However, if the challenge were successful, it could have consequences for all corporations that have filed or must file IS 2025 using those models.
Economic and operational impact
At this time, the direct economic impact is undetermined: it depends on the outcome of the judicial proceedings. However, there are two scenarios that companies should keep in mind:
- If the challenge is dismissed: the IS 2025 models maintain full validity and there is no operational change. Declarations filed or to be filed are completely valid.
- If the challenge is upheld: the National Court could annul the Order HAC/529/2026 in whole or in part, which would require Finance to approve new models and could affect declarations already filed. The specific implications would depend on the scope of the ruling.
The immediate operational impact is the 9 business day deadline to intervene. Companies with complex tax situations or that believe the instructions of Order HAC/529/2026 harm them should urgently assess whether it is in their interest to join the proceedings as an interested party.
Who does it affect?
- All commercial corporations required to file Corporate Income Tax for fiscal year 2025.
- Non-resident entities subject to Non-Resident Income Tax (IRNR) for the same fiscal year, since Order HAC/529/2026 also regulates their declaration models.
- Companies with complex tax situations or that have had difficulties applying the instructions of the models approved by Order HAC/529/2026.
- Consolidated groups and entities with special tax structures that may be affected by the outcome of the litigation.
- Tax advisors and consulting firms that manage IS 2025 declarations for their clients and must monitor the development of the proceedings.
Practical example
Imagine a mid-sized corporation, Distributions XYZ, SL, that filed its IS 2025 declaration in July 2026 using the models approved by Order HAC/529/2026. During completion, its advisor detected that certain model instructions generated interpretive doubts that could harm the company.
When the summons is published on September 29, 2026, Distributions XYZ, SL has 9 business days to decide whether to intervene in challenge 998/2026 as an interested party. If it does, it can defend its position in the proceedings and directly benefit from a potential upholding of the challenge. If it does not act within that deadline, it will lose the opportunity to be a party to the litigation, although it could still be affected by the outcome if the ruling has general effects.
The decision to intervene requires hiring a lawyer qualified before the National Court and assessing whether the cost of the proceedings justifies the potential benefit.
What should companies do now?
- Verify the deadline urgently: the summons was published on September 29, 2026. Calculate the 9 business days from that date to know when the intervention deadline expires. After that time, it is not possible to join as a party.
- Assess whether legitimate interest exists: consult with your tax advisor whether your company has any specific situation linked to the instructions of Order HAC/529/2026 that justifies intervening in the challenge (discrepancies in the application of the models, damages derived from its instructions, etc.).
- Contact a lawyer specialized in tax administrative litigation: intervention before the National Court requires legal representation. If you decide to act, do so before the deadline expires.
- Monitor the development of the proceedings: even if you do not intervene, monitor challenge 998/2026. If the court upholds the challenge, Finance will have to approve new models and declarations already filed could be affected.
- Maintain the obligation to file IS 2025: while the challenge is pending, the models remain valid. Do not suspend or delay the filing of your declaration for this reason.
Frequently asked questions
What is challenge 998/2026 and what exactly does it challenge?
Administrative litigation 998/2026 has been filed by Inverama, SL before the Second Section of the Administrative Litigation Chamber of the National Court. It challenges Order HAC/529/2026, of May 7, which is the regulation that approves the official declaration models for Corporate Income Tax and Non-Resident Income Tax for the tax periods of fiscal year 2025.
How much time do I have to intervene in the challenge against IS 2025 models?
You have 9 business days from the publication of the summons in the BOE, which took place on September 29, 2026. After that deadline, it is not possible to join the proceedings as an interested party. If you have doubts about whether it is in your interest to act, consult with a lawyer specialized in tax litigation as soon as possible.
Should I stop filing my IS 2025 declaration while the challenge is pending?
No. While the challenge is pending, Order HAC/529/2026 and the models it approves remain fully valid and mandatory. You must file your IS 2025 declaration within the usual deadlines using the current models. Only if the court upheld the challenge and annulled the order would Finance be required to approve new models.
What would happen if the National Court upholds the challenge and annuls the IS 2025 models?
If the court upheld the challenge, Order HAC/529/2026 could be annulled in whole or in part. This would require the Ministry of Finance to approve new declaration models. The specific implications for declarations already filed would depend on the scope of the judicial ruling. Companies with complex tax situations or affected by the order's instructions are those with the greatest interest in closely monitoring the proceedings.
What companies have legitimate interest to intervene in challenge 998/2026?
Any person or entity that could be affected by the outcome of the litigation has the right to intervene. In practice, this especially includes corporations that have had difficulties applying the instructions of the models approved by Order HAC/529/2026, entities with complex tax situations, or those that believe the order's instructions harm them. The specific assessment should be made by a tax advisor or tax lawyer.
Official source
Consult complete regulation at official source
Notice: 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-2026-20244
