France is the fourth-largest source of posted workers into Belgium, and French companies are strongest in exactly the sectors where site registration bites: electrical installation, metalworks and pipefitting, and petrochemical maintenance. A shared border and a shared language make the administrative side feel familiar, which is precisely why the Belgian-specific formalities get missed.
Where France sits in the Belgian market
French companies filed for 19,352 posted persons into Belgium in 2023, 8.3 percent of the Limosa total, and the figure has been rising steadily. French firms account for 15 percent of posting companies in electrical installation and assembly, 13 percent in metalworks and pipefitting and 12 percent in the petrochemical industry. French nationals are the top nationality of posted workers in Belgium’s electrical installation and assembly sector.
The flow runs both ways, and heavily: France is the single largest destination for workers posted out of Belgium, receiving 41 percent of Belgian-issued A1 documents under Article 12. If your business already handles inbound Belgian subcontractors, do not assume the outbound formalities mirror them.
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 the Caisse Primaire d’Assurance Maladie (CPAM) before departure, one per posted worker, covering the full planned period. They prove your people stay in the French 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.
Assuming the French detachement file covers Belgium
French companies are used to a mature domestic posting regime and often assume that a properly constituted detachement file travels. It does not. The French declaration satisfies French obligations. Belgium requires its own notification, filed in Belgium, before the work starts.
The second recurring issue is the liaison person. Belgium requires you to give the Labour Inspectorate the identity and contact details of a person who can be reached about the posting. French companies frequently name a head-office contact who is unreachable during Belgian site hours, which turns a routine check into an escalation.
Third, watch the sector. Electrical installation and petrochemical turnaround work is high-value and almost always crosses the 500,000 euro threshold that triggers Check-in-at-Work, even when your own scope is a fraction of the total. The threshold applies to the works, not to your contract.
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 sets out the liability your Belgian client carries for your crews.
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 Cegelec manages registration across Belgian sites.
A note on language
French is an official Belgian language, so correspondence in Wallonia and Brussels is straightforward. In Flanders, however, the administrative language is Dutch, and a Flemish site inspection will be conducted in Dutch. If your crews work north of the language border, plan for that rather than assuming French will be accommodated.
For everything a foreign employer needs before sending crews across the border, see the full guide for companies posting workers to Belgium.
Book a free demo
If you are bringing French 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.
