Slovenia is a top-ten source of posted workers into Belgium, and by some distance the most striking case of a sending country whose postings are mostly not its own nationals. Only 10 percent of persons posted from Slovenia to Belgium are Slovenian. That single statistic defines the compliance profile.
Where Slovenia sits in the Belgian market
Slovenian companies filed for 5,593 posted persons into Belgium in 2023, 2.4 percent of the Limosa total, placing Slovenia ninth among sending countries despite its size.
The nationality breakdown is unusual: 33 percent are Bosnians and Herzegovinians, 13 percent Kosovars, 12 percent Serbians and only 10 percent Slovenians. Bosnians posted from Slovenia into Belgian construction is one of the main third-country posting routes into Belgium, at 1,916 people in 2023.
The four things you must have
Work backwards from your mobilisation date, because two of these depend on third parties.
1. A1 certificates, applied for at ZZZS, the Health Insurance Institute of Slovenia before departure, one per posted worker, covering the full planned period. They prove your people stay in the Slovenian social security system rather than becoming liable for Belgian contributions. See what Belgian inspectors check on an A1. 2. A Belgian company number (CBE) and portal access, if Check-in-at-Work will apply. Foreign employers need both to register presence at all, and this is the step most often left too late. 3. The Limosa declaration, filed at limosa.be before the first day of work. It produces a LIMOSA-1 receipt each worker must be able to show to the Belgian client. Full detail in our Limosa guide. 4. A liaison person, whose identity and contact details you give to the Belgian Labour Inspectorate, and who can actually be reached about the posting.
Does the A1 replace the Limosa declaration?
No, and this is the most expensive misunderstanding in cross-border work.
The A1 answers which country’s social security system applies. Limosa answers whether Belgium knows your worker is on its territory. They are issued by different bodies for different purposes. An employer holding a valid A1 still has to file a Limosa declaration before the work starts, and an inspector will ask for both.
Third-country nationals are the whole story
For a Slovenian posting company, the A1 and the Limosa declaration are the easy part. The harder part is evidencing that each third-country national on the crew is lawfully resident and lawfully employed in Slovenia, which is what allows them to be posted onward into Belgium.
Belgian inspections of Slovenian crews commonly become residence and work authorisation checks. The Court of Justice of the European Union addressed residence requirements for posted third-country nationals in its judgment of 20 June 2024 in Case C-540/22 (SN and Others), and Belgian enforcement in this area is active.
Build a three-part file for every posted worker: the A1 from ZZZS, the LIMOSA-1, and documentation of lawful residence and employment in Slovenia. A crew whose Belgian paperwork is perfect but whose Slovenian residence documentation is incomplete will still fail the inspection.
When does Check-in-at-Work apply?
Registration is mandatory for works on immovable property, excluding cleaning, and for certain meat-sector activities, where the total value of the works reaches 500,000 euro excluding VAT. The threshold applies whether that value is reached at the start of the works or during them, and it attaches to the works as a whole, not to your own contract value.
Three points that catch foreign contractors:
- It is daily. Registration must happen before the person begins work, every working day, for every person on site. It is not a one-off enrolment.
- Responsibility is shared. It lies both with the party sending the worker and the party doing the work, and the two must agree who registers and verify it happened. Assuming the main contractor covers you is not a defence.
- “Works on immovable property” is broad, reaching well beyond new-build into renovation, fit-out, technical installation and groundworks.
From 1 April 2027, a Programme Law adopted on 30 May 2026 extends the obligation to registering both entry and exit, and brings the supply of ready-mixed concrete into scope. Sign-in sheets will not carry you past that date.
The differences between the systems are set out in Limosa, Dimona or Check-in-at-Work.
What it costs to get wrong
Failing to file a Limosa declaration is a level 4 offence, the heaviest category in the Belgian Social Criminal Code, carrying the possibility of imprisonment alongside financial penalties.
Fines rose on 1 February 2026, when the Act of 19 December 2025 raised the multiplier applied to social criminal fines from 8 to 10. For some infringements the amount is multiplied by the number of workers involved, up to a maximum of 100, which is what turns one administrative gap on a ten-person crew into a serious figure.
There is a commercial cost too. Your Belgian client is exposed through joint and several liability for your workers’ wages, and through the withholding obligation: where a contractor has social or tax debts, the client must withhold 35 percent of each invoice excluding VAT for social security debts and 15 percent for tax debts, checked at checkinhoudingsplicht.be. Since 1 May 2026 a further 15 percent applies for outstanding self-employed contributions. A subcontractor who creates that problem does not get invited back. Our guide for main contractors explains why clients ask foreign subcontractors for documents.
Keeping the paperwork and the site in agreement
The hard part of cross-border work is not understanding the rules. It is keeping the file in your home office and the reality on a Belgian site aligned, week after week, as crews rotate and programmes move.
Two habits do most of the work. Treat every crew change as a compliance event: a new person means a new A1 check, a new Limosa entry and site registration under their own identity, arranged before they travel. And capture presence digitally at the moment someone arrives, tied to the person and the project, so the site record matches your declarations by default and you can produce a specific past day on request without reconstructing it.
Suivo’s check-in-at-work is used on Belgian sites where several subcontractors work side by side, and runs on the same workforce management platform as time tracking, so the data you capture for compliance also feeds hours and project costing instead of sitting in a separate system.
See how B&R Bouwgroep manages registration across Belgian sites.
A note on language
Slovenian is not an administrative language in Belgium. Correspondence and inspections are in Dutch, French, German or English, so plan your liaison person accordingly.
If your workers travel from several countries, the complete guide for employers posting into Belgium covers each of them.
Book a free demo
If you are bringing Slovenian crews onto Belgian sites and want presence registration that satisfies an inspector without slowing your work down, we will show you how it runs day to day. Book a free demo.
