A mid-sized German manufacturing group with a Polish subsidiary had been tracking KSeF developments for over a year. When the Ministry of Finance confirmed the phased mandatory rollout schedule, the German parent's finance director called with a single question: "Which deadline applies to us, and what happens if we miss it?" The answer was not simple. It depended on the subsidiary's revenue, its VAT registration status in Poland, and whether it had already integrated with the National e-Invoicing System (Krajowy System e-Faktur, KSeF).

Under Polish tax law, mandatory KSeF participation follows a two-phase timeline. Companies with annual turnover exceeding PLN 200 million must comply from 1 February 2026. All remaining VAT-registered taxpayers follow from 1 April 2026. Missing either deadline exposes a company to financial penalties of up to PLN 100 per non-compliant invoice, with no statutory cap on the aggregate amount.

This case study traces how we guided a German group through the KSeF deadline timeline for 2026–2027: mapping which threshold applied, restructuring internal invoice flows, and embedding the system before the compliance window closed. The lessons apply equally to any foreign-owned entity operating in Poland.

What was the background for this German group?

The Polish subsidiary operated as a limited liability company registered with the National Court Register (Krajowy Rejestr Sądowy, KRS). Its annual Polish-source turnover sat just below PLN 200 million – placing it in the second compliance tier, with an April 2026 deadline. However, the parent company issued cross-border intra-group invoices to the Polish entity. Those invoices raised a separate question: did the German parent's Polish VAT registration trigger an independent KSeF obligation?

It did. The Polish Financial Supervision Authority (Komisja Nadzoru Finansowego, KNF) framework is not directly relevant here, but the Tax Administration Chamber (Izba Administracji Skarbowej) confirmed in written guidance that a foreign entity registered for VAT in Poland must issue KSeF-compliant invoices for its Polish-taxable supplies. The German parent held a Polish VAT number for reverse-charge purposes. That registration brought it within the February 2026 threshold – not April – because the consolidated group revenue, assessed at the Polish VAT registration level, exceeded PLN 200 million.

This distinction caught the client off guard. Two separate compliance deadlines now applied within the same corporate group: February for the German parent's Polish VAT number, April for the subsidiary. The gap between those dates was only 59 days. In practice, that meant running parallel implementation tracks simultaneously.

How did we structure the compliance strategy?

The first step was a diagnostic mapping of every invoice flow touching the Polish VAT registrations. We identified three distinct categories: domestic B2B invoices issued by the subsidiary, intra-group invoices from the German parent to the subsidiary, and reverse-charge invoices where the subsidiary was the buyer. Each category carried different KSeF treatment. Domestic B2B invoices required immediate KSeF issuance. Intra-group flows needed an agreed XML structure. Reverse-charge invoices fell outside the mandatory KSeF scope for the issuing party but still required a KSeF reference number on the buyer's records.

We then coordinated with the client's ERP provider to configure the KSeF API connection. The Ministry of Finance's test environment had been available since mid-2025. We used it for a six-week integration sprint, running live invoice simulations against the production schema. This approach – which we also outline in our compliance programme design guide for Germany subsidiaries in Poland – reduced the risk of schema errors surfacing after the mandatory go-live date.

We secured a reversal of a preliminary penalty assessment exceeding PLN 180,000 for a manufacturing client in the Mazowieckie region (autumn 2025), where the tax authority had treated test-environment invoices as non-compliant production invoices. That precedent shaped how we documented the German group's testing phase: every test transaction was logged with a timestamp and a written declaration that it fell outside the mandatory period.

What were the critical process steps and timeline?

The implementation unfolded across four distinct phases. First, in September 2025, we completed the legal audit: confirming which Polish tax law provisions applied to each entity, verifying the turnover threshold calculation, and obtaining a written confirmation from the tax office regarding the German parent's February 2026 obligation. This confirmation took 30 days to arrive and proved essential when the authority later queried the group's self-assessment.

  • September–October 2025: legal audit and threshold confirmation
  • November–December 2025: ERP configuration and test-environment integration
  • January 2026: parallel-run period for the German parent's VAT number
  • February 2026: mandatory go-live for the parent's Polish invoices
  • April 2026: mandatory go-live for the subsidiary's domestic invoices

The parallel-run period in January 2026 was the most operationally demanding phase. The German finance team had to issue invoices simultaneously in their domestic SAP system and through the KSeF API. We assisted in drafting an internal protocol that assigned responsibility for each invoice type to a named individual. Accountability gaps – not technical failures – are the most common cause of KSeF non-compliance in foreign-owned groups. Our broader Polish tax practice consistently flags this as the first risk to address.

Our team obtained interim protection for a German investor's subsidiary in Lower Silesia (spring 2026) by securing a suspension of a penalty proceeding while the client demonstrated that its KSeF invoices had been issued within the permitted 1-day offline window. That matter reinforced the importance of understanding the offline tolerance rules: if the KSeF system is unavailable, a taxpayer may issue an invoice outside the system but must upload it within 1 business day of reconnection.

What lessons transfer to other German companies with Polish operations?

The most transferable lesson is threshold awareness. German groups frequently assume that only the Polish subsidiary's turnover counts. In reality, a separate Polish VAT registration – even held solely for reverse-charge or import-VAT purposes – carries its own KSeF obligation. If that registration's associated revenue crosses PLN 200 million at the group level, the February 2026 deadline applies, not April.

Transfer pricing documentation also intersects with KSeF in a way that surprises many clients. Intra-group invoices that are later adjusted through transfer pricing corrections must be re-issued or corrected through KSeF. The correction invoice (faktura korygująca) must carry the original KSeF reference number. Groups that handle transfer pricing adjustments outside their ERP – through manual journal entries – will need to change that practice. For more context on how KSeF interacts with cross-border VAT structures, our note on what KSeF means for businesses in Slovakia provides a useful comparative frame.

Finally, the IP Box regime and Polish tax incentives do not reduce KSeF obligations. Some clients mistakenly believe that preferential tax treatments – IP Box, R&D relief, or the family foundation structure – create carve-outs from the invoicing mandate. They do not. KSeF applies to all VAT-registered taxpayers within scope, regardless of which tax optimisation structures the entity uses. A tax advisor Warsaw-based or Warsaw-advising should confirm this point early in any compliance review.

Frequently asked questions

Q: Does a German company with only a Polish VAT number – and no physical presence – need to comply with KSeF?

A: Yes, if the company issues invoices for supplies that are taxable in Poland and it is registered as a VAT taxpayer in Poland. The KSeF obligation attaches to the VAT registration, not to a permanent establishment or physical address. The applicable deadline depends on the turnover threshold assessed at the level of that registration.

Q: How long does a typical KSeF integration take for a mid-sized foreign subsidiary?

A: In our experience, a realistic integration timeline runs 10 to 14 weeks from the start of the legal audit to the first live KSeF invoice. ERP configuration typically accounts for six to eight of those weeks. Starting after October 2025 for the February 2026 deadline leaves very little margin for error.

Q: Can a Polish subsidiary use a third-party KSeF service provider instead of direct API integration?

A: Yes. Polish tax law permits taxpayers to authorise a third party – an accounting firm or a dedicated invoicing platform – to issue and receive KSeF invoices on their behalf. The authorisation must be registered in the KSeF system. The taxpayer remains liable for any non-compliant invoices issued by the authorised party, so contractual protections and service-level commitments are essential.

Specific KSeF compliance situations require individual legal and tax assessment. Missing the applicable deadline forfeits the right to issue standard VAT invoices and exposes the entity to per-invoice penalties with no aggregate cap. To receive an expert assessment of your group's KSeF readiness, contact info@kordeckipartners.com.

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 VAT 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.