A Polish company sending workers to a Belgian construction site needs four things in place before day one: A1 certificates from ZUS for every posted worker, a Limosa declaration filed before work starts, a named liaison person communicated to the Belgian Labour Inspectorate, and, on qualifying sites, working access to Check-in-at-Work for daily presence registration. Each one is separate, and having three of the four still leaves you in breach on the fourth.
Key takeaways
- Before day one, a Polish company needs A1 certificates from ZUS, a Limosa declaration, a named liaison person and, on qualifying sites, Check-in-at-Work registration.
- An A1 does not replace Limosa: the A1 covers social security, Limosa tells Belgium your worker is there, and inspectors ask for both.
- Check-in-at-Work applies every day, before work starts, on works on immovable property worth 500,000 euro excluding VAT or more.
- Failing to file a Limosa declaration is a level 4 offence, the heaviest category in the Belgian Social Criminal Code.
The sequence, in order
Work backwards from your mobilisation date, because two of these steps depend on third parties and cannot be rushed.
1. A1 certificates, from ZUS. Apply in Poland, to the Polish institution, before departure. The A1 proves your workers remain in the Polish social security system, so you do not owe Belgian contributions for them. Processing takes time, so this is the first thing to start, not the last. Read what Belgian inspectors check on an A1.
2. Check-in-at-Work access. Without a Belgian company number (CBE) or portal access, you can still register presence by scanning the QR code on each worker’s LIMOSA-1 in the mobile Check-in-at-Work service, but that route only registers: it cannot consult or cancel a registration. Full access needs secure access to the Belgian social security portal, which requires a CBE number and a main access manager with a Belgian national register or BIS number. That takes time to arrange, so start early.
3. Limosa declaration. Filed online at limosa.be before the work begins, once per worker per posting, covering an anticipated duration of up to 24 months. You receive a LIMOSA-1 receipt immediately, and each worker must be able to produce it to the Belgian client. Full detail in our Limosa guide.
4. 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. Choose someone who answers their phone and speaks a language the inspectorate can work in.
5. Presence registration from day one. Not from the first invoice, not once the site settles down. Day one.
Does an A1 mean you can skip Limosa?
No. This is the most common and most expensive misunderstanding among posting companies, and it is worth being blunt about.
The A1 answers which country’s social security system applies. Limosa answers whether Belgium knows your worker is on its territory. An employer holding a valid A1 for a posted worker still has to file a Limosa declaration. They are issued by different bodies, for different purposes, and an inspector will ask for both.
When does Check-in-at-Work apply to you?
Registration is mandatory for works on immovable property, excluding cleaning, where the total value of the works reaches 500,000 euro excluding VAT. The threshold applies whether the value is reached at the start of the works or during them. The delivery of ready-mixed concrete and certain meat-sector activities are covered too; for the meat sector no minimum amount applies.
Three things Polish contractors regularly get caught by:
- It is daily. Registration must happen before the person begins work, every working day, for every person. It is not a one-off site enrolment.
- Responsibility is shared, not delegated by assumption. It lies both with the party sending the worker and the party doing the work. You and the main contractor must agree who registers and verify that it happened. “We thought the Belgian contractor was registering our people” is a finding, not a defence.
- “Works on immovable property” is broad. It reaches well beyond new-build: renovation, fit-out, technical installation fixed to a building and groundworks commonly fall inside it.
From 1 April 2027, a Programme Law adopted on 30 May 2026 extends the obligation to registering both entry and exit, for works on immovable property and for the supply of ready-mixed concrete, which is already in scope today. If your current method is signing a sheet at the gate, plan the change now.
The differences between the systems are set out in Limosa, Dimona or Check-in-at-Work.
Are any of your trips exempt?
Possibly, but the exemptions are narrower than they look. Short technical visits can qualify: initial assembly or installation of goods you supplied is exempt for a maximum of 8 days, but this exemption does not apply to the construction sector. Urgent repair or maintenance by specialised technicians, of machines or equipment their employer delivered, is exempt for a maximum of 5 days per month.
Both limits are hard. A commissioning problem that pushes an installation to day nine removes the exemption entirely, and you are then in the position of having failed to declare. If an assignment might overrun, declare it. Filing costs nothing. The full list with every threshold is in Limosa exemptions.
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, with the possibility of imprisonment alongside financial penalties.
Fines increased on 1 February 2026 under the Act of 19 December 2025, which 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 a single administrative gap on a twelve-person crew into a serious figure.
There is also a commercial cost that does not appear in any penalty schedule. 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 30 October 2026, clients in construction and cleaning also withhold 15 percent where the contractor has unpaid self-employed social contributions. A subcontractor whose paperwork creates that problem does not get invited back. Our guide for main contractors explains how Belgian clients screen their subcontractors.
What an inspection on a Belgian site looks like
Belgian social inspectors do not only check that documents exist. They check that documents match reality:
- The worker in front of them is the worker named on the A1 and the Limosa declaration, spelling included.
- The employer on the paperwork is the employer actually directing the work.
- The dates cover today.
- The declared site and client match where they are standing.
- Today’s presence registration exists for this person.
The findings that hurt are almost never deliberate. They are crew substitutions nobody updated, projects extended without revisiting certificates, and attendance records that cannot be produced for a specific past date.
Making it hold together across the border
The hardest part of Polish-to-Belgian posting is not understanding the rules. It is keeping the paperwork in Poland and the reality on a Belgian site in agreement, week after week, when crews rotate and programmes move.
Two practices make the difference. First, treat every crew change as a compliance event: new worker means new A1 check, new Limosa entry, new site registration, before they travel. Second, capture presence digitally, at the moment someone arrives, tied to the person and the project. That gives you a record that matches your declarations by default, produces a specific day’s attendance on demand, and does not depend on a foreman remembering to collect a sheet.
Suivo’s check-in-at-work is used on Belgian sites where several subcontractors work alongside each other, and it runs on the same workforce management platform as time tracking, so the data you capture for compliance also feeds your hours and project costing rather than sitting in a separate system.
See how Cegelec manages registration across multiple Belgian sites.
A note on language
Belgian inspections and official correspondence are in Dutch, French or German, depending on the region, not in Polish. Make sure the person handling your declarations and your named liaison person can work in the relevant language, or appoint a representative in Belgium who can.
If you run crews from more than one country, our guide to every declaration Belgium expects covers them together.
Frequently asked questions
What does a Polish company need before posting workers to Belgium?
You need A1 certificates from ZUS for every posted worker, a Limosa declaration filed before work starts and a liaison person whose details are passed to the Belgian social inspection. On sites that fall under Check-in-at-Work, every person must also be registered each working day before starting work.
Do posted workers with an A1 certificate still need a Limosa declaration?
Yes. The A1 shows which country’s social security system applies, while Limosa tells Belgium that your worker is on its territory. They are issued by different bodies for different purposes, and a Belgian inspector will ask for both.
When does Check-in-at-Work apply to foreign contractors in Belgium?
Check-in-at-Work is mandatory for works on immovable property, excluding cleaning, when the total value of the works reaches 500,000 euro excluding VAT, and for certain meat-sector activities. Every person must be registered every working day before work begins. Clients, contractors, subcontractors and employers all have registration duties, and so do the workers themselves.
What is the penalty for not filing a Limosa declaration?
Failing to file a Limosa declaration is a level 4 offence, the heaviest category in the Belgian Social Criminal Code, with possible imprisonment on top of fines. For offences from 1 February 2026 the fine multiplier rose from 8 to 10, and the fine is multiplied by the number of workers involved, up to a maximum of 100.
Book a free demo
If you are bringing Polish 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.
