Starting January 1, 2026, businesses in Poland will be allowed to attach supporting documents—such as specifications or product details—to structured invoices submitted through the KSeF system, using the FA(3) schema. To use this feature, companies must notify the tax office via the e-Tax Office and ensure their software supports the new format, as attachments carry cybersecurity considerations and must be properly managed.
Poland: Attachments to Structured Invoices in KSeF Coming January 2026
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Poland
Author: Ivana Picajkić
Category:
Fiscal subject related
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450
Content accuracy validation date:
11.06.2025
Content accuracy validation time:
08:42h
Starting January 1, 2026, businesses in Poland will be able to attach files to structured invoices in the National e-Invoice System (KSeF). This functionality is designed to help companies document more complex transactions, where additional materials, such as service specifications or product breakdowns, are often included.
Many businesses already send attachments alongside their invoices. These supporting documents, while useful, are not considered part of the invoice itself. With the upcoming KSeF update, companies will be able to legally and officially include these attachments within the structured invoice system. Attachments will be supported using the FA(3) invoice schema.
How will it work?
- Start Date: January 1, 2026,
- Eligibility: Any business using KSeF with compatible accounting or ERP software.
Requirements:
- Companies must report their intention to send attachments via the e-Tax Office (e-Urząd Skarbowy),
- The software used must support the FA3 schema.
This reporting process is important for cybersecurity. Since attachments may carry risks such as malware or unauthorized data, the system requires prior notification to protect against abuse and cyberattacks.
Businesses are encouraged to:
- Ensure their accounting or ERP software is up to date and compliant with the FA3 standard,
- Submit notification to the tax office if they plan to use attachments,
- Monitor the Ministry of Finance’s website for official technical documentation, expected in the second half of 2025.
Companies using InsERT software, such as Subiekt nexo or Rachmistrz nexo, are already being supported. These systems are continuously updated to align with regulatory changes and are expected to be fully compatible with the new KSeF requirements.
Now is the ideal time for companies to review their systems, begin planning, and ensure compliance ahead of the 2026 deadline.
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