As of 1 January 2026, the Polish Ministry of Finance enables taxpayers to issue and send structured invoices with attachments via KSeF 2.0. This functionality is optional, but it comes with strict registration, technical and content rules. Companies planning to use attachments should prepare in advance and align their process and systems with these requirements.
This update builds on earlier steps in Poland’s KSeF transition, including the confirmed KSeF 1.0 shutdown timeline and the broader rollout approach for KSeF 2.0. For background and timeline context, see: Poland confirms KSeF 1.0 shutdown timeline ahead of KSeF 2.0, Poland KSeF update for February 2026, and Poland prepares for the KSeF era.
Registration via the e-Tax Office
To issue invoices with attachments in KSeF 2.0, taxpayers must first register their intention through the e-Tax Office. The registration is submitted as a formal notification and is processed within a maximum of three working days.
The notification requires the following information:
- Taxpayer identification details
- A contact email address
- The type of activities for which invoice attachments will be used, such as utilities or telecommunication services
- Technical parameters, including the estimated average monthly number of invoices and their average size in kilobytes
Once the notification is approved, the taxpayer receives confirmation by email. Only after this confirmation can invoices with attachments be issued in KSeF 2.0.
Who can submit the notification
Notifications can be submitted by:
- Individual taxpayers using their NIP tax identification number
- Non-individual taxpayers, such as companies, via an authorised organisational account user
The authorisation model mirrors other KSeF access rights and must be in place before the notification can be submitted.
What attachments are allowed in KSeF 2.0
Attachments must be an integral part of the structured XML invoice file. Only content that is directly related to tax data is permitted.
Allowed attachments include data that:
- Supports or explains tax-related information on the invoice
- Is strictly connected to the invoicing transaction
The following are explicitly not allowed:
- Separate or unstructured files
- Marketing or promotional content
- Contracts or agreements
- Acceptance or delivery protocols
- Price lists or general documentation
Attachments cannot be used as a workaround to transmit non-invoice information via KSeF.
Compliance risks and loss of functionality
The Ministry of Finance makes it clear that misuse of attachments can lead to consequences. If a taxpayer does not comply with the attachment rules, the right to issue and send invoices with attachments may be revoked.
Taxpayers can also voluntarily submit a notification to stop using invoice attachments. In that case, the functionality is formally disabled.
What this means for companies preparing for KSeF 2.0
The attachment functionality offers flexibility for specific use cases, but it also introduces additional compliance responsibilities. Companies should assess whether attachments are required for their invoicing scenarios and ensure that both content and technical setup remain within the defined limits.
As KSeF 2.0 moves towards mandatory adoption, this update underlines the broader direction of structured, controlled and auditable e-invoicing in Poland.
Key takeaways
Changes companies need to implement when using invoice attachments in KSeF 2.0 include:
- Registering attachment usage in advance via the e-Tax Office
- Defining eligible invoicing scenarios and technical parameters
- Ensuring attachments are embedded in the XML and strictly tax-related
- Preventing the use of attachments for contracts, marketing or other non-invoice content
- Monitoring compliance to avoid loss of attachment rights
