CIUS (Core Invoice Usage Specification)

A formally documented restriction of the European semantic e-invoice standard EN 16931, published by CEN/TC 434. A CIUS allows a Member State, public administration, or industry sector to make EN 16931 stricter for its context — but never looser. Any invoice valid under a CIUS is automatically valid under EN 16931; the reverse is not guaranteed.

What it is

A CIUS narrows the EN 16931 core invoice data model through one or more of the following restrictive amendments (VATupdate, 2026-07-01; ec.europa.eu, 2026-02-02):

Making optional elements mandatory
Narrowing cardinalities (e.g., reducing maximum repetitions)
Restricting allowed code list values to a subset
Adding validation business rules consistent with the core model

A CIUS may never add new business terms, widen semantic definitions, or introduce logic that contradicts the core model. Doing any of those creates an Extension — a different category with stricter interoperability consequences.

The technical methodology for creating a CIUS is specified in CEN/TR 16931-5:2017 (ec.europa.eu, 2026-02-02).

The BT-24 identifier

Every invoice claiming conformance with a specific CIUS must carry the Specification Identifier (business term BT-24) in the EN 16931 data model. This field signals to recipients which CIUS rules apply. A CIUS must be registered in the EC eInvoicing Community registry before its BT-24 identifier can be legitimately used (ec.europa.eu, 2026-02-02; peppol.org, last modified 2022-04-03).

CIUS vs. Extension vs. National format

Type	Adds new business terms?	EN 16931-compliant?	Example
CIUS	No — restriction only	✅ Yes	XRechnung, Peppol BIS 3.0, NLCIUS
Extension	Yes — adds terms	❌ Not by itself	ZUGFeRD EXTENDED profile
National format	Often — predates EN 16931	❌ No	FatturaPA (Italy)

A buyer who only accepts an extended or proprietary invoice format is not considered EN 16931-compliant (ec.europa.eu, 2026-02-02). The hierarchy is unambiguous: EU law → national VAT law → technical standards; legal requirements prevail over specifications (VATupdate, 2026-07-01).

Legal framework

Two instruments give CIUS their legal standing (VATupdate, 2026-04-13; VATupdate, 2026-07-01):

Directive 2014/55/EU — obliges Member States to ensure contracting authorities can receive EN 16931-compliant e-invoices. CIUS are the mechanism by which Member States implement this obligation while adding national requirements.
Commission Implementing Decision (EU) 2017/1870 — published the reference to EN 16931 in the Official Journal, formally making it the European standard for e-invoicing.

Governance: CEN/TC 434

CEN/TC 434 (European Technical Committee for e-invoicing standards) sets the rules for CIUS creation, publication, and maintenance. A CIUS must (VATupdate, 2026-07-01):

Be documented and publicly available
Be registered in the EC eInvoicing Community registry
Clearly identify which business rules it restricts, which code lists it narrows, and which cardinalities it modifies

EN 16931 is an 8-part standard series maintained by CEN/TC 434 (VATupdate, 2026-04-13).

EN 16931-1:2026 update (ViDA-ready)

On 13 February 2026, CEN approved an updated version — EN 16931-1:2026 — incorporating ViDA (VAT in the Digital Age)-driven requirements for B2B structured e-invoicing and digital reporting. Key changes include (RTC Suite, 2026-02-20; VATupdate, 2026-04-13):

Supplier bank account (IBAN) becomes a mandatory field (to support tax authority financial flow tracking)
Explicit indication of triangulation simplification
Clearer rules on corrective invoice sequencing
Stronger treatment of foreign currency cases
Support for carrying XML attachments in structured flows

This update means all national CIUS must eventually align to the new EN 16931-1:2026 base — Germany's KoSIT is planning XRechnung 4.0 for this purpose (peppol.helger.com, undated) (as-of 2026-07-31).

Technical mechanism: the 4-level validation stack

An invoice sent via Peppol into a national clearance platform typically passes through four independent validation layers (VATupdate, 2026-07-01):

EN 16931 core rules — validates the semantic model itself
Peppol BIS CIUS rules — Peppol-specific additions (e.g., mandatory electronic addresses)
National CIUS rules — country-specific restrictions (e.g., Leitweg-ID for Germany)
Platform-specific rules — additional requirements from the receiving platform or tax authority

Each layer can independently reject an invoice. EN 16931 compliance alone is insufficient for national mandate compliance.

National CIUS implementations across Europe

Germany: XRechnung

Germany's national CIUS of EN 16931, maintained by KoSIT. Mandatory for all B2G invoices since November 2020. Current version: 3.0.2 (Winter 2025/26 Bugfix), containing 147 XRechnung validation rules (as-of 2026-07-31) (invoicenavigator.eu, last verified March 2026; VATupdate, 2026-05-25).

XRechnung adds 21 BR-DE semantic business rules beyond EN 16931, including the mandatory Leitweg-ID — a routing identifier required for German government invoices. Supports two syntax variants: UBL 2.1 and UN/CEFACT CII.

Germany's B2B e-invoicing mandate timeline (as-of 2026-07-31) (invoicenavigator.eu, March 2026):

Phase	Date	Obligation
Phase 1	January 2025	Receive structured EN 16931-compliant e-invoices (all businesses)
Phase 2	January 2027	Issue for domestic B2B (turnover >€800,000)
Phase 3	January 2028	Issue for domestic B2B (all remaining businesses)

See full detail: XRechnung.

Peppol BIS Billing 3.0

The globally most-adopted CIUS, developed by OpenPeppol AISBL. In use in 40+ countries (as-of 2026-07-31) (invoicenavigator.eu, undated). OpenPeppol makes the Buyer and Seller Electronic Address identifier mandatory (not mandatory in the EN 16931 core) to enable routing via the Peppol eDelivery Network (peppol.org, last modified 2022-04-03).

Updated semi-annually (May and November releases). Current release: November 2025 (as-of 2026-07-31) (docs.peppol.eu, 2025-11).

Conformance with Peppol BIS implies conformance with EN 16931; conformance with EN 16931 does not imply conformance with Peppol BIS (VATupdate, 2026-07-01).

Belgium mandated Peppol BIS 3.0 for all B2B e-invoicing from January 2026, transmitted exclusively via the Peppol network, including country-specific rounding rules on top of the base CIUS (Global VAT Compliance YouTube, 2026-02-18; fiskaly.com, 2025-10-08) (as-of 2026-07-31).

Netherlands: NLCIUS and SI-UBL

NLCIUS (Netherlands Core Invoice Usage Specification) is the Dutch CIUS of EN 16931, defining additional mandatory fields for e-invoices to Dutch public authorities (labelled BR-NL rules). SI-UBL 2.0 is the technical UBL 2.1 implementation. B2G mandatory since January 2017. No B2B mandate as of mid-2026 (klippa.com, 2026-02-18) (as-of 2026-07-31).

NLCIUS and Peppol BIS 3.0 are related but distinct: NLCIUS defines content requirements; Peppol defines transport; they have differences in rules and validations at the detailed level (klippa.com, 2026-02-18).

Austria: CIUS-AT-GOV and CIUS-AT-NAT

Austria has two national CIUS specifications — CIUS-AT-GOV (for government invoices) and CIUS-AT-NAT (for private sector use) — both limiting UBL and CII syntaxes. Also supports ebInterface and Peppol BIS 3.0 (ecosio.com, 2024-01-19; fiskaly.com, 2025-10-08) (as-of 2026-07-31).

Portugal: CIUS-PT

Portugal's national specification; QR code embedding became mandatory from January 2026. No full B2B e-invoicing mandate as of 2025 (fiskaly.com, 2025-10-08).

Italy: FatturaEU (CIUS-IT) vs. FatturaPA

Italy's formal EN 16931 CIUS — CIUS-IT ("FatturaEU") — exists and is accepted by Italy's SDI clearance platform, but it is rarely used in practice. The dominant domestic format remains FatturaPA, which uses a proprietary XML schema (v1.2, technical specifications v1.9 as of April 2025) structurally incompatible with UBL and CII, predating EN 16931 (invoicenavigator.eu, March 2026; EC Italy Country Sheet 2025).

Italy processes over 2 billion invoices per year through the SDI (as-of 2026-07-31) (invoicenavigator.eu, March 2026). The European Council authorised Italy to continue operating the SDI through December 31, 2027 (invoicenavigator.eu, March 2026).

France

France accepts three formats — UBL, CII, and national Factur-X — rather than a single CIUS. B2B mandate for large and mid-size businesses to receive invoices: September 2026. SME issuing deadline: September 2027 (fiskaly.com, 2025-10-08).

The EDICOM France e-invoicing webinar (est. Feb 2026) describes the French reform as "one of the most complex models at an international level" due to simultaneous e-invoicing and e-reporting obligations (EDICOM YouTube, est. 2026-02-24).

Other countries (2026 mandates)

(as-of 2026-07-31; fiskaly.com 2025-10-08)

Country	Format/CIUS	Mandate
Denmark	Peppol BIS 3.0 + OIOUBL	B2B from January 2026
Croatia	Peppol BIS 3.0, UBL 2.1, CII	B2B from January 2026
Poland	Proprietary FA(3) XML	B2B from Feb 2026 (large) / Apr 2026 (all)

ViDA and the harmonisation paradox

ViDA (VAT in the Digital Age) positions EN 16931 as the reference semantic model for Digital Reporting Requirements for intra-EU B2B transactions from 2028. The result is a two-speed architecture: convergence on the intra-EU reporting data model; continued divergence on domestic invoicing via proliferating national CIUS (VATupdate, 2026-07-01).

Under ViDA, buyers will no longer be able to refuse EN 16931-compliant e-invoices, eliminating the historical "buyer acceptance" requirement for electronic formats (VATupdate, 2026-04-13) (as-of 2026-07-31).

The paradox: EN 16931 was designed to enable cross-border interoperability, yet the very mechanism that allows Member States to adopt it — the CIUS — is also the mechanism that reintroduces divergence. The more CIUS proliferate, the more effective interoperability of the core standard is reduced (VATupdate, 2026-07-01).

CIUS are also insufficient for Continuous Transaction Control (CTC) environments: a business aligned with all applicable CIUS but that has not addressed platform rules, reporting extracts, and invoice lifecycle events will not be compliant under CTC regimes (VATupdate, 2026-07-01).

EC policy trajectory (2025–2026)

As of March 2026, 21 EU countries have introduced B2G e-invoice issuing obligations (as-of 2026-03-31) (ec.europa.eu, 2026-03-31).
May 2025: the European Commission announced plans to make eInvoicing an accounting software module requirement, and to replace the current B2G Directive with a Regulation mandating the European standard for public procurement — planned for Q4 2026 (as-of 2026-07-31) (ec.europa.eu, 2026-03-31).

Key terms

Term	Meaning
CIUS	Core Invoice Usage Specification — a formally documented restriction of EN 16931
EN 16931	The European e-invoice semantic standard (8-part CEN series)
BT-24	The Specification Identifier business term in EN 16931, used to signal which CIUS applies
Extension	An instrument that adds business terms outside EN 16931; not EN 16931-compliant by itself
CEN/TC 434	The CEN technical committee that maintains EN 16931 and governs CIUS registration
Leitweg-ID	Germany's routing identifier for B2G e-invoices; unique to XRechnung
SI-UBL	The Dutch UBL 2.1 implementation of NLCIUS
SDI	Italy's Sistema di Interscambio — clearance platform through which all Italian e-invoices pass
CIUS-IT	Italy's formal EN 16931 CIUS (FatturaEU); rarely used in practice
FatturaPA	Italy's dominant domestic e-invoice format; proprietary; predates EN 16931

Next frontiers (dangling links)

Factur-X — France's hybrid PDF/XML format; closely related to ZUGFeRD; referenced here
Peppol BIS 4.0 — next-generation Peppol CIUS incorporating PINT and EN 16931-1:2026
Continuous Transaction Control (CTC) — clearance model that CIUS cannot address on its own
CIUS FNFE — France's formal CIUS registration; details not retrieved
NLCIUS — Dutch CIUS; warrants its own page
ebInterface — Austrian format referenced alongside CIUS-AT