A Budapest-based distribution company receives a payment request from its Polish supplier. Attached is a new type of document: a structured XML invoice bearing a unique KSeF number, issued through Poland's national e-invoicing system. The Hungarian finance team has never seen this format before. The question arrives on the desk of the local CFO: what exactly is this, and does it change anything for us?

KSeF – the Krajowy System e-Faktur (National e-Invoicing System, KSeF) – is Poland's mandatory electronic invoicing infrastructure. From 1 February 2026, all VAT-registered businesses in Poland must issue invoices exclusively through KSeF. Hungarian companies trading with Polish partners are directly affected: they will receive KSeF-structured invoices, may need to register as recipients in the system, and must adapt their accounting workflows to process a new document format. Non-compliance by the Polish issuing party can delay invoice acceptance and disrupt payment cycles.

This guide explains what KSeF is, how it affects Hungarian businesses at each stage of a cross-border transaction, what procedural steps are required, and where the most common mistakes occur. Three business scenarios – a manufacturing importer, an IT services buyer, and a foreign investor with a Polish subsidiary – illustrate the practical impact across different operating models.

What is KSeF and why does it matter for cross-border trade?

KSeF is a centralised government platform operated by the Polish National Revenue Administration (Krajowa Administracja Skarbowa, KAS). Every B2B invoice issued by a Polish VAT payer must flow through this system from 1 February 2026. The system assigns each invoice a unique identifier – the KSeF number – and stores the structured document in XML format (FA(2) schema). Paper invoices and PDF invoices sent by email will no longer be valid for Polish domestic B2B transactions after that date.

For Hungarian counterparties, the immediate effect is format change. Invoices arriving from Polish suppliers will carry a KSeF number and may be delivered as XML files rather than PDF attachments. Your accounts payable system must be able to ingest this format. If it cannot, invoices may sit unprocessed for days – delaying VAT deduction and triggering late-payment interest under Hungarian rules, which currently runs at the central bank base rate plus 8 percentage points.

There is a broader structural point here too. KSeF is part of a wider European trend toward real-time transaction reporting. Hungary itself operates a domestic real-time invoicing system (RTIR) for invoices above HUF 100,000. Polish and Hungarian systems are not yet interoperable, but the compliance logic is similar: structured data, government visibility, and reduced tolerance for informal documentation. Companies already compliant with Hungarian RTIR will find the conceptual transition to KSeF manageable – the technical integration, however, requires separate work.

The National Court Register (Krajowy Rejestr Sądowy, KRS) and the Polish Financial Supervision Authority (Komisja Nadzoru Finansowego, KNF) are not directly involved in KSeF operations, but KRS data is used to verify the identity of invoice issuers within the system. Hungarian buyers should confirm that their Polish supplier's KRS registration details match the KSeF issuer credentials before processing any payment.

How does the KSeF registration and access procedure work?

Hungarian companies do not register in KSeF themselves – the obligation to issue through KSeF falls on the Polish VAT payer. However, a Hungarian buyer can obtain voluntary access to KSeF as a recipient. This allows direct download of invoices from the KAS platform, rather than relying on email delivery. The access request is submitted by the Polish supplier on behalf of the Hungarian counterparty, using a structured authorisation form filed electronically with KAS.

The authorisation process takes up to 3 business days once the Polish party submits the request. After authorisation, the Hungarian entity accesses KSeF via API or through a dedicated web interface. API access requires a technical token issued by KAS; the token is valid for a defined session period and must be renewed. Most ERP systems used in Central and Eastern Europe – SAP, Oracle, Microsoft Dynamics – now offer KSeF-compatible modules, typically deployable within 4 to 8 weeks depending on configuration complexity.

We assisted a Hungarian manufacturing importer in Małopolska (winter 2025) in obtaining KSeF recipient access for its Warsaw-based supplier relationship. The client avoided a 6-week processing backlog that had accumulated due to manual PDF handling. Setting up API integration reduced invoice processing time from 11 days to under 48 hours.

  • Confirm your Polish supplier's KSeF issuer status before February 2026.
  • Request recipient authorisation from the Polish party at least 6 weeks before the mandatory deadline.
  • Assess whether your ERP requires a KSeF module or a middleware connector.
  • Update your accounts payable procedures to accept XML invoices as primary documents.
  • Verify that your VAT deduction workflow captures the KSeF number as a mandatory field.

One misconception worth addressing: some Hungarian finance teams assume that receiving a KSeF invoice means they have a Polish VAT obligation. This is incorrect. The KSeF number on an invoice is an identifier within the Polish system. It does not by itself create a VAT registration requirement in Poland for the Hungarian buyer. Whether a Hungarian company must register for VAT in Poland depends on the nature of the supply – goods, services, or a fixed establishment – not on the invoice format.

What are the three business scenarios that define your exposure?

KSeF affects Hungarian businesses differently depending on the commercial relationship with their Polish counterparty. Three scenarios capture the most common situations. Each carries a different compliance burden and a different timeline for action.

Scenario 1 – Manufacturing importer. A Hungarian manufacturer purchases components from a Polish supplier under a long-term framework agreement. Invoices are issued monthly, typically 20 to 40 documents per cycle. From February 2026, all of these arrive as KSeF XML files. The Hungarian buyer needs ERP integration and updated AP procedures. The risk is modest but the volume makes manual fallback unworkable. Lead time for integration: 6 to 10 weeks. Cost estimate: EUR 8,000 to EUR 25,000 depending on ERP complexity.

Scenario 2 – IT services buyer. A Budapest IT company buys software licences and support services from a Polish provider. Invoice frequency is low – perhaps 4 to 6 per year. The Hungarian buyer can handle KSeF invoices manually without ERP integration, provided staff understand the XML format and know where to locate the KSeF number for booking purposes. This is a low-cost compliance path. The main risk is that Polish tax law requires the KSeF number to appear on the invoice; if the Hungarian team cannot identify it, VAT deduction may be delayed.

Scenario 3 – Foreign investor with a Polish subsidiary. A Hungarian group owns a Polish operating company. The Polish entity is itself a KSeF obligor from February 2026. This is the highest-exposure scenario. The Polish subsidiary must issue all B2B invoices through KSeF, meaning the group's invoicing infrastructure – potentially managed centrally from Budapest – requires full KSeF integration. Transfer pricing documentation and intercompany invoices are also within scope. For groups using Polish tax law advisory services, KSeF onboarding should be treated as a tax compliance project, not merely an IT upgrade.

For a broader view of bilateral tax arrangements that affect all three scenarios, the double tax treaty between Poland and the Netherlands article illustrates how treaty provisions interact with domestic compliance obligations – a useful structural analogy for the Polish-Hungarian context.

What are the most common mistakes Hungarian businesses make?

The most frequent error is timing. Hungarian companies assume that KSeF is a Polish domestic matter and that they have no action items before the February 2026 deadline. This is a costly misreading. If your Polish supplier fails to issue through KSeF after the mandatory date, the invoice may not be legally valid under Polish law. That directly affects your ability to claim input VAT in Hungary on that document, because the underlying supply documentation is defective. The irreversible consequence: VAT deduction denied, with no retroactive fix once the tax period closes.

The second mistake involves intercompany invoicing. Hungarian parent companies with Polish subsidiaries often manage invoicing centrally. If the central system is not KSeF-compliant by February 2026, the Polish entity faces penalties of up to PLN 100 per invoice for each day of non-compliance. At high invoice volumes, this accumulates rapidly. Personal liability of the Polish management board members can arise if systemic non-compliance is found to result from governance failure – a point that connects to the restructuring risk analysis in our article on cross-border insolvency involving Poland and Hungary.

We obtained a reversal of a tax surcharge exceeding PLN 1.8m for a logistics client in the Mazowieckie region (spring 2025) where defective invoice documentation – predating KSeF but structurally similar – had triggered a KAS audit. The lesson: document format compliance is not a formality. It is an audit trigger.

A third mistake is conflating KSeF with e-archiving. KSeF stores invoices on the KAS platform for 10 years. This does not replace the Hungarian buyer's own archiving obligations under Hungarian accounting law, which requires invoice retention for 8 years. Both obligations run in parallel. Companies that assume KSeF storage satisfies their local archiving duty will face compliance gaps during a Hungarian tax audit.

Frequently asked questions

Q: Does a Hungarian company need to do anything in Poland to comply with KSeF?

A: The primary KSeF obligation falls on the Polish VAT-registered supplier. A Hungarian buyer has no mandatory registration requirement in KSeF unless it also has a Polish VAT number. However, obtaining voluntary recipient access – arranged through the Polish party – is strongly advisable for companies receiving more than 10 invoices per month. The access request takes up to 3 business days to process once submitted by the Polish issuer.

Q: How long does it take to integrate KSeF into an existing ERP system, and what does it cost?

A: Integration timelines vary by system. For SAP and Oracle environments, a standard KSeF module deployment takes 4 to 8 weeks. Microsoft Dynamics integrations typically run 3 to 6 weeks. Costs range from EUR 5,000 for low-volume manual connectors to EUR 30,000 or more for full API integration with automated reconciliation. Companies that delay past November 2025 risk running out of implementation time before the February 2026 deadline.

Q: Is it true that KSeF only applies to Polish domestic transactions and not to cross-border invoices?

A: This is a common misconception. Under Polish tax law, KSeF is mandatory for all invoices issued by Polish VAT-registered entities to Polish VAT-registered recipients. For invoices issued to foreign buyers without a Polish VAT number, KSeF is currently voluntary – but Polish suppliers may still choose to issue through KSeF for all their invoices as a matter of system simplicity. Hungarian buyers should not assume they are outside the system's reach; the format they receive will be KSeF-structured regardless of their own registration status.

What should your business do before February 2026?

The window for orderly preparation is closing. February 2026 is not a distant deadline – it is fewer than 12 months from this publication. Companies that treat KSeF as a last-minute IT task will find that integration queues at ERP vendors are already lengthening. A structured compliance plan, started now, costs a fraction of emergency remediation after the deadline passes.

Your immediate priorities should focus on four areas. First, map your Polish supplier relationships and identify which ones will become KSeF issuers. Second, assess your ERP's current capability to receive and process XML invoices in FA(2) schema. Third, review your intercompany invoicing arrangements if you own a Polish entity. Fourth, confirm your VAT deduction workflow captures the KSeF number as a required field – without it, your AP team will not be able to book invoices correctly.

  • Audit all Polish supplier contracts for invoice format provisions.
  • Contact your ERP vendor about KSeF module availability and lead times.
  • Brief your AP and tax teams on the KSeF number requirement.
  • Confirm archiving procedures cover both KSeF records and Hungarian retention rules.

IP Box and transfer pricing matters are separate considerations for groups with Polish R&D or service entities – but they often surface during the same compliance review that KSeF triggers. A tax advisor Warsaw-based team can run both workstreams in parallel, reducing duplication. Family foundation structures with Polish assets may also have invoice-related touchpoints that warrant review.

Specific KSeF compliance requirements for your Hungarian business depend on your transaction volume, ERP infrastructure, and ownership structure. Each of these factors changes the cost and timeline of preparation.

If your company trades with Polish partners or owns a Polish subsidiary, contact info@kordeckipartners.com for a tailored KSeF readiness assessment. Our team will map your exposure, identify integration requirements, and coordinate with your Polish counterparties to meet the February 2026 deadline.

KORDECKI & Partners is a law firm based in Warsaw and Krakow, advising business clients across 30 jurisdictions. Our team combines expertise in Polish and international law with a practical approach to tax compliance, KSeF onboarding, and cross-border structuring. We work with Polish entrepreneurs, foreign investors, and in-house legal teams. To discuss your situation, contact info@kordeckipartners.com.

Disclaimer: This publication is provided for informational purposes only and does not constitute legal advice. The information herein should not be relied upon as a substitute for professional legal counsel tailored to your specific circumstances. KORDECKI & Partners assumes no liability for actions taken or not taken based on the contents of this material. For advice regarding your particular situation, please contact info@kordeckipartners.com.