At the beginning of November, the Ministry of Finance published a new draft law introducing significant changes to the functioning of e-invoices in Poland. The most important change is the update to the FA(3) schema version, which will allow attachments to be included with invoices. In a previous article, we discussed the other amendments in general (link). Today, we will focus on the new attachment functionality. 

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1. Why were attachments introduced?

The introduction of attachments to e-invoices in KSeF is a response to numerous requests from entrepreneurs, particularly those who need to include more detailed data with their invoices. This is especially relevant for information regarding energy and gas consumption, details of telecommunication services, or data related to fuel sales. 

2. What will attachments to invoices in KSeF look like? 

An attachment to an invoice will be an integral part of the invoice (it will not be a separate file). The Zalacznik (Attachment) node will appear in the schema only once, but within this node, taxpayers will be able to submit up to 1,000 data blocks (i.e., effectively 1,000 different attachments). 

Each data block can be completed in one of three ways: 

  • In dictionary format: providing values in two simplified columns (max. 1,000 occurrences), 
  • In text format: with a maximum of 5,120 characters, 
  • In tabular format: allowing data entry into a table of up to 20 columns and 1,000 rows, enabling detailed representation of information such as units of measurement, quantities of goods, or unit prices. 

It is important to note that adding attachments is not mandatory. If this format does not meet a taxpayer’s needs, they can send an attachment to the invoice recipient in another way, such as via email. 

3. What should not be included in attachments? 

According to the Ministry of Finance, attachments are not intended to convey purely commercial, marketing, or business-related information. Therefore, the following should not be included: 

  • price lists, warranty conditions, user manuals, 
  • orders, contracts, contract amendments, acceptance protocols, 
  • information on promotions, sales, individual offers, or newsletters. 

Additionally, attachments in PDF or JPG formats will not be supported. Such attachments will continue to be transmitted outside KSeF as they have been so far. 

4. Who Can Send an Attachment to KSeF? 

Anyone! Although the Ministry of Finance has emphasized the particular usefulness of attachments for businesses in the fuel, telecommunications, and utilities sectors, their use is not restricted to any specific industries. 

But first, a notification must be submitted…

The ability to send attachments to invoices will only be available after submitting a notification via the KSeF API. An entrepreneur wishing to use this option must submit a request, which must include justification for the need to send attachments and an estimated number of attachments per month. 

The notification will be reviewed within 30 days, during which the taxpayer will receive an API communication granting permission to send attachments. It is advisable to plan ahead—if you want to use attachments from the first available day (1st February 2026), you should submit your request by the end of December 2025. 

…And attachments can only be sent via API

Sending e-invoices with attachments will only be possible using the API. This means that taxpayers using free tools provided by the Ministry of Finance (such as Aplikacja Podatnika KSeF or e-mikrofirma) will not be able to send attachments through KSeF. 

5. KSeF – what should you consider now? 

Implementing KSeF is a multi-stage and complex process that requires a combination of tax, legal, system, and process knowledge. Although the mandatory transition to KSeF is just over a year away, experience shows that implementing such a solution within a company often takes more than 12 months. Therefore, now is a good time to start preparations if business process planning has not yet begun. For many taxpayers, the obligation to use KSeF will coincide with the mandatory JPK CIT reporting, increasing the need to plan resources and implementation schedules. 

The team of experts at CRIDO, combining specialists in business, technology, and tax law, has successfully completed nearly 100 projects supporting clients in preparing for KSeF implementation.