New due diligence obligation in Flanders: chain liability for the illegal employment of third-country nationals

The concept of chain liability

The principle of chain liability when illegally employing third-country nationals is not new in Belgium: the Act of 30 April 1999 on the employment of foreign workers already provided for such a mechanism.

In general, chain liability means that every link in a contracting chain can be held liable where a (sub)contractor employs third-country nationals residing illegally in Belgium, whether as employees or as self-employed persons.

Reminder: the already existing rules on chain liability in Flanders

Where a client, main contractor or intermediary contractor has only an indirect relationship with the relevant (sub)contractor, liability arises only if it was aware in advance that the (sub)contractor employed illegally residing third-country nationals. The burden of proving this awareness rests with the inspection authorities.

Where the relationship is direct, liability arises automatically unless the client, main contractor or intermediary contractor obtained a written declaration from its direct (sub)contractor before the works started, confirming that it does not, and will not, employ illegally residing third-country nationals. Even holding this declaration does not protect a party that was in fact aware of the illegal employment.

These existing rules continue to apply in every industry.

What is new: the additional due diligence obligation in high-risk industries and activities

The Flemish legislator has added a further layer on top of the existing regime for a defined list of high-risk industries and activities, namely:

• the construction industry;
• the cleaning industry;
• the meat industry; and
• postal deliverers working on behalf of postal services.

In these high-risk industries and activities, since 1 January 2026, a client, main contractor or intermediary contractor can only exclude chain liability towards a direct (sub)contractor if it satisfies both the existing written declaration requirement and the new active due diligence obligation. Holding the declaration alone is no longer sufficient in these industries and activities.

The due diligence obligation has four elements:

1. Document collection before works start. Depending on the situation of the foreign employee or self-employed person (posting from the EEA or Switzerland, posting from outside the EEA, or direct employment in Belgium), the client or contractor must collect specific documents, such as a passport or travel document, proof of valid residence, an A1 declaration or Limosa registration, a combined permit or work authorisation and, for direct Belgian employment, proof of Dimona registration.
2. Visual assessment of authenticity. The documents must be checked to confirm that they appear genuine and are not obviously forged. No forensic verification is required, but validity dates must always be checked. Documents that are clearly forged or expired are treated as equivalent to having no documents at all.
3. Retention of the documents. The documents must be kept for at least five years after the collaboration ends, so that they can be produced to the social inspectorate on request.
4. Follow-up on deficiencies. Where documents are missing, forged or invalid, the direct (sub)contractor must be asked to provide correct documents. If it does not respond, a report must be filed with the Flemish Social Inspectorate through the designated portal.

Liability is excluded only where all four steps are completed. Even then, a party that actually knew about the illegal employment remains liable, regardless of the declaration and due diligence steps taken.

A de minimis threshold applies: the due diligence obligation does not apply to construction works worth less than EUR 30,000 (excl. VAT) carried out by a contractor without subcontractors, or to works worth less than EUR 5,000 (excl. VAT) involving only one subcontractor.

Non-compliance can trigger criminal and administrative sanctions.

Collecting and sharing these documents raises clear GDPR questions. The Flemish legislation provides an explicit legal basis for the client to request the documents and for the (sub)contractor to provide them.

Documents should not be provided in redacted form. The purpose of the legislation is to prevent and combat illegal employment, so the client must be able to verify that the individual concerned is lawfully resident and lawfully working in Belgium. Redacting identifying details, such as a name or the validity dates of a residence or work permit, would defeat that purpose.

Separately, the GDPR transparency obligation requires that affected employees be informed that their personal data will be processed for this purpose, which in practice means updating the privacy notice issued to employees.

Alongside the statutory steps, we recommend strengthening your contracts with direct (sub)contractors operating in the high-risk industries and activities. Recommended clauses include for example:

• a confirmation that the subcontractor does not, and will not, employ illegally residing third-country nationals;
• a requirement on the direct (sub)contractor to include the same clause in contracts with any further subcontractors;
• an obligation to provide the required documents and an audit right;
• an indemnity in favour of the client or main contractor should illegal employment nevertheless occur; and
• a right to terminate the agreement immediately and without compensation if illegal employment is discovered.