E-Invoicing: Is Your SME Ready?

If you supply goods or provide services to government bodies, municipalities, or public institutions, this article is for you. Digital transformation within the Public Administration and efforts to combat tax evasion have introduced new structural requirements for B2G (Business-to-Government) transactions. In 2026, Portugal is in a crucial regulatory transition period that directly affects how Small and Medium-Sized Enterprises (SMEs) manage their invoicing processes.

Understanding the current deadlines, mandatory formats such as CIUS-PT, and how to avoid penalties or payment rejections from public entities requires agile and up-to-date tools. This is where Moloni ON comes in, providing an invoicing solution designed to simplify your company’s tax obligations with the Portuguese Tax and Customs Authority (AT).

Key Takeaways

• Extended deadlines in 2026: According to the latest regulations and the 2026 State Budget, digitally signed PDF invoices continue to be legally accepted as electronic invoices until 31 December 2026.
• The turning point (2027): From 1 January 2027, the transitional period ends for micro, small, and medium-sized enterprises supplying the public sector. Structured electronic invoicing becomes mandatory.
• CIUS-PT standard: B2G electronic invoices must comply with the structured XML format under the European CIUS-PT (UBL 2.1) standard and be transmitted through Electronic Data Interchange (EDI) platforms or approved communication networks.
• Mandatory validation elements: The ATCUD (Unique Document Code) and QR Code remain mandatory on all issued documents to ensure fiscal traceability.
• Moloni ON as your partner: The transition to XML invoicing and automated SAF-T (PT) reporting is handled natively through the Moloni ON ecosystem, eliminating the need for complex and costly integrations.

What changes for Public Sector E-Invoicing in 2026?

If your company works with public contracts, the key word for 2026 is preparation. While large companies have been operating under mandatory structured e-invoicing requirements since 2021, implementation deadlines for SMEs have been postponed several times due to technical complexity and implementation costs across the Portuguese business landscape.

Throughout 2026, the final transitional regime remains in force. This means your SME can continue sending invoices in PDF format to public entities, provided that those invoices comply with AT certification requirements and include a qualified digital signature.

However, this is the final opportunity to modernize your invoicing infrastructure. Sending a simple PDF by email will no longer be sufficient for public procurement purposes, and businesses should begin preparing immediately for the transition to structured electronic invoicing.

What is the final transition deadline for SMEs?

Large Companies

• January 2021 Mandatory use of structured electronic invoices (CIUS-PT) in public procurement contracts.

PDF Invoice Acceptance

• December 2026 Final deadline for PDF invoices to be accepted as equivalent electronic invoices, provided digital signature requirements are met.

Full SME Compliance

• 1 January 2027 Mandatory use of structured CIUS-PT XML invoicing for micro, small, and medium-sized enterprises supplying public entities.

What is the CIUS-PT format and why isn’t a PDF enough?

This is one of the most common questions among Portuguese business owners modernizing their operations.

A PDF sent by email is not considered a valid B2G electronic invoice under the final compliance regime. A PDF is essentially a digital representation of a document that still requires manual processing by the recipient.

True electronic invoicing requires a structured XML format based on the European Standard EN 16931, adapted in Portugal as CIUS-PT (UBL 2.1).

This structured data file allows public sector accounting systems to automatically read, validate, and process invoices without human intervention. If your invoicing software cannot generate and transmit these structured files through approved channels, your invoices may be rejected by government platforms such as FE-AP, managed by eSPap.

What technical requirements are mandatory for valid invoices?

To issue legally compliant invoices in Portugal—whether for B2B or B2G transactions—your business must comply with strict requirements established by the Portuguese Tax and Customs Authority. There is no room for shortcuts.

What are the risks and penalties for non-compliance?

Ignoring the transition to structured electronic invoicing can lead to much more than administrative inconvenience; it can have serious financial and operational consequences for your SME.

The first risk is invoice rejection. If you submit an invoice that does not comply with FE-AP specifications or the requirements of the public entity’s electronic invoicing intermediary, the document will be automatically rejected. Public institutions are legally prohibited from processing payments based on invalid invoices.

As a result, payment delays can become chronic, directly affecting your cash flow.

Additionally, issuing invoices without mandatory elements such as the ATCUD code or using non-certified software may result in substantial penalties imposed by the Portuguese Tax and Customs Authority. Depending on the size of the company and the severity of the infringement, fines can reach several thousand euros.

How can your SME prepare for E-Invoicing with Moloni ON?

Digital transformation does not have to be expensive or dependent on complex IT consultancy projects. The most effective strategy is to adopt modern cloud-based solutions that automate compliance behind the scenes.

Moloni ON makes this transition simple and intuitive. Designed for business agility, it enables you to manage the entire sales cycle from any device or screen.

How to Migrate and Ensure Compliance

1. Update Your Company Information

Initial Setup

Ensure all your company’s tax information is up to date in Moloni ON. Configure your invoicing series so the system can automatically obtain ATCUD validation from the Portuguese Tax Authority.

2. Configure Public Sector Customers

Foco no Setor Público

When registering public entities (ministries, municipalities, hospitals, or other government organizations), ensure all required identification details are entered, including public procurement identifiers and organization-specific codes.

3. Activate the Electronic Invoicing Module

CIUS-PT Integration

Enable integration with approved electronic invoicing distribution networks within the software ecosystem. This ensures that when you issue an invoice, the system automatically converts the information into a structured XML file that complies with the CIUS-PT standard.

4. Automate SAF-T Reporting

Monthly Compliance

Configure automated submission or simplified extraction of the SAF-T (PT) invoicing file, ensuring communication with the Portuguese Tax Authority occurs within the legally established deadlines and reducing the risk of reporting errors.

Management Tip: Start Before the Deadline. Do not wait until the final days of 2026 to begin this transition.By adopting structured electronic invoicing and testing your B2G integrations during 2026, your SME gains a significant competitive advantage when participating in public tenders and procurement opportunities. The sooner your systems are aligned with CIUS-PT requirements, the smoother your transition into the fully digital public procurement environment of 2027 will be.