The draft regulation of the Minister of Finance dated May 21, 2025, introduces detailed regulations regarding the use of attachments to e-invoices in the National e-Invoice System (KSeF). The new provisions, which will enter into force on January 1, 2026 (one month before the mandatory implementation of KSeF), precisely define notification procedures and technical requirements for this functionality.

Have a question or need support?

Contact us

Notification procedure – faster than expected

The regulation introduces a significantly faster procedure than originally planned. The Head of the National Tax Administration has only 3 business days to confirm the notification of intention to issue e-invoices with attachments. This is a significant difference compared to earlier assumptions about a 30-day application processing period.

The notification must be submitted through the e-Tax Office before starting to issue e-invoices with attachments. Entrepreneurs planning to use this functionality from the first day of mandatory KSeF implementation (February 1, 2026) should submit their notification in January 2026, taking into account the several-day processing time.

Specific categories of business activity

The regulation precisely defines which types of business activities may use attachments. These are primarily entities from certain industries that, during the KSeF 1.0 stage, advocated for the necessity of developing an attachment containing complex data regarding units of measure, quantities (numbers) of delivered goods or performed services, and unit prices of goods or services. In the current wording of the regulation, the entrepreneur must indicate that the issued e-invoices document:

  • supplies of electricity, thermal or cooling energy, and piped gas
  • provision of telecommunications services
  • provision of energy distribution services
  • fuel deliveries at vehicle stations for a given settlement period
  • other activities requiring detailed description

Key is the submission of a declaration that the invoices concern ‘activities with a complex number of data regarding units of measure and quantities of delivered goods or performed services, unit prices of goods or services without tax amounts’.

Two-year validity period and update obligation

Permission to issue invoices with attachments is valid for 2 years from the date of receiving confirmation. Extension requires submitting a new notification. Additionally, the taxpayer is obligated to update the notification in case of changes in the scope of documented activities, the expected number of invoices with attachments, or their average size.

Risk of permission withdrawal

The regulation provides for the possibility of permission withdrawal by the Head of the National Tax Administration in cases of abuse. This applies to cases where the attachment does not contain extensive data regarding quantities, measures, or unit prices, has a marketing character, or contains prohibited content. This is an important warning for entrepreneurs planning to use attachments for purposes other than substantive supplementation of invoice data.

Technical requirements and limitations

An e-invoice with an attachment must be issued in XML format and may contain only one attachment constituting an integral part of the e-invoice. The maximum size of the entire e-invoice with attachment is 3 MB. The functionality will be available only after acceptance of the notification by the e-Tax Office and provision of appropriate functionality in KSeF.

Certain documents will still require separate transmission outside the KSeF framework, including CMR consignment notes, customs documents, and acceptance protocols.

Implications for the invoicing process

The introduction of attachments affects the KSeF implementation process, which already requires significant preparations from enterprises. Companies must not only adapt their financial and accounting systems to handle the new FA(3) schema version but also redesign business processes related to document flow.

Early planning is crucial for determining which invoices will need attachments and their required format. These decisions will influence software provider selection, ERP system setup, and staff training requirements. Businesses should also verify that their planned attachments comply with permitted functionality guidelines, or identify alternative approaches if needed.

Prepare today!

The regulations regarding attachments enter into force on January 1, 2026, which means that notifications can be submitted from the beginning of 2026, so that from February 1, 2026, taxpayers will be ready to issue e-invoices according to their needs.

Entrepreneurs interested in using attachments should already prepare for the notification procedure and verify whether their planned use of this functionality falls within the framework of permitted business activity categories.

Our CRIDO expert team has extensive experience in KSeF implementation and can help you with comprehensive preparation for new requirements. Contact us to discuss an implementation strategy tailored to your industry specifics and business needs.