Under CIaO, everyone who works on the site registers their own presence, including the employees of subcontractors, the self-employed and temporary workers. As a contractor, however, you must make sure that your employees, your subcontractors and their employees can actually register. As a client, your main risks lie in Limosa and joint and several liability.
CIaO (Check in and out at Work) becomes mandatory on 1 April 2027 for work on immovable property of 500,000 euros or more excl. VAT and for the delivery of ready-mixed concrete. On such a site, several companies often work side by side: a main contractor, specialised subcontractors, self-employed workers, temporary workers and sometimes foreign teams.
The NSSO has not yet published every detail on how responsibilities are shared under CIaO for construction. Below we list what is already certain today.
In this article you will read what duties each role in the chain has, how to let temporary and foreign workers register, what the declaration of works requires when you subcontract, when you become jointly and severally liable and which agreements you should put in your contracts.
Who is responsible for registration in the chain?
The pillar page on the CIaO obligation gives a short overview of who is responsible. Here we go deeper, role by role. The basic NSSO rule: employers, contractors and contracting parties make sure that their employees, their subcontractors and the employees of those subcontractors are registered.
That does not mean you register everyone yourself. Each person registers themselves, in real time, at the workplace; the employer may not register anyone in advance or remotely. Your task is to make sure registration is possible. In practice, the NSSO asks for four things:
- Provide a registration system, or agree on an alternative together with your subcontractor.
- Make sure the data are correctly transmitted to the NSSO.
- Supply a compatible registration tool, such as an app or a system connected to CIaO through the NSSO web service.
- Inform your staff about how and when they must register.
| Role | Main duties | Watch out |
|---|---|---|
| Main contractor (declaring contractor) | Makes sure own employees, subcontractors and their employees can register, and files the declaration of works | Since 29 June 2026, only this contractor can create or change the declaration of works |
| Subcontractor | Has the same duty for its own employees and for its own subcontractors | Informs the declaring contractor in advance before bringing in subcontractors of its own |
| Self-employed person with own subcontractors | Falls under the same rules as an employer and also checks in and out personally | Subcontractors without staff must also be listed in the declaration of works |
| Temporary work agency and user company | The user company provides the registration tool or sets out the registration method in a contract | For the 30bis declaration, the agency counts as a subcontractor of the user company |
| Employee or temporary worker | Registers personally, in real time, on arrival at and departure from the workplace | The employer may not enter attendance in advance or remotely |
Through the NSSO web service you can also consult the attendance of your staff and of your subcontractors. That way, as a contractor, you keep sight of what happens further down the chain.
According to the explanation of the scheme, anyone who meets their obligations is not liable when an employee still forgets to register, makes a mistake or refuses. How to get employees on board and what to do about a forgotten registration is covered in introducing CIaO and getting employees on board
Who has temporary workers register: the agency or the user company?
The user company, in other words the business where the temporary worker is placed. According to the NSSO, an organisation that uses a temporary worker must provide the registration tool, or set out the registration method in a contract.
This fits the way the NSSO views the chain. For the declaration of works (article 30bis), the temporary work agency counts as a subcontractor of the user company, and the user company reports the attendance. The link between temporary worker, agency and user company runs through the Dimona declaration.
In practice, this comes down to three agreements:
- Agree in writing with the agency which registration tool the temporary worker uses and who explains how it works.
- Check at the start that the Dimona declaration for the temporary worker is in order, because it carries the link with your company.
- Give the temporary worker the same registration tool as your own team, so there is only one way of working on site.
What applies to foreign subcontractors and workers?
When you work with a foreign employer or self-employed person, three files come together: Limosa, CIaO and a European reform that is not yet in force.
Limosa: ask for the proof and report what is missing
A foreign employer or self-employed person must show you, as the Belgian client, a Limosa-1 certificate. If you do not receive it, you report this yourself through the online service Limosa Notification Duty, electronically and before work starts. That report does not release the foreign employer from its own notification duty. Checking the certificate via the QR code with Check Limosa is optional.
CIaO: a separate procedure has been announced
Under the current Checkinatwork scheme, foreign workers register by scanning the QR code on their Limosa-1. For CIaO, the NSSO states that foreign workers and self-employed persons will follow a specific procedure, but the details are not yet known. In its advice of 2 June 2026, the High Council points out that foreign workers without a registration device find it hard to register, and calls for sector solutions.
In practice: ask foreign subcontractors now how their people will register on site from 1 April 2027, and provide a solution for anyone without a suitable smartphone.
Europe: mandatory prior notification and A1, but not yet today
The revision of the European social security coordination rules makes prior notification and an A1 application mandatory for posting. In construction, this applies even to jobs of one or two days. However, the regulation still has to be published in the Official Journal of the EU, and most rules only apply two years after entry into force. So nothing changes today and Limosa still applies.
Do not confuse this with another European file. On 23 June 2026, the Council and Parliament reached a provisional agreement on a voluntary EU interface for digital posting declarations. Member states decide for themselves whether to use it instead of their national system.
What must you report in the declaration of works when you subcontract?
The declaration of works (30bis) is filed by the contractor hired by the client. It is mandatory from 30,000 euros excl. VAT, or from 5,000 euros as soon as there is at least one subcontractor, and must be made before work starts. From 1 April 2027, Catena replaces the current service for the chain declaration, while attendance runs through Check in and out at Work.
For the chain, these rules matter most:
- A subcontractor that wants to bring in its own subcontractors must inform the declaring contractor in advance.
- Subcontractors without staff, such as a self-employed person working alone, are also listed in the declaration.
- Service providers such as surveyors, safety coordinators and engineering firms are not listed as subcontractors, unless they carry out work on immovable property themselves.
- Failing to file the declaration risks a penalty of 5% of the total amount excl. VAT of the unreported works.
When are you jointly and severally liable for your subcontractor?
Joint and several liability means you can be held responsible for another company's debts. In construction, this plays out in three areas: social security debts, tax debts and wage debts.
Social security and tax debts: withholding on the invoice
If you work with a (sub)contractor that has social security debts, you can become jointly and severally liable. You avoid this by withholding 35% of the invoice amount and paying it to the NSSO. For tax debts, the withholding is 15%. So check the databases of the NSSO and of the FPS Finance when you sign the contract, and again during execution.
Wage debts: after a notice from the inspectorate
For wages in construction (general scheme), joint and several liability starts 14 working days after a notice from the inspectorate and lasts for a maximum of one year. Three rules apply:
- Whoever is jointly and severally liable posts a copy of the notice at all workplaces of the employer concerned.
- You can limit your liability to the work performed for your benefit, or prove that few or no hours were worked.
- If the inspectorate cannot establish the work performed, a flat rate based on the minimum wage applies.
Not a legal rule, but practical advice: compare your subcontractors' CIaO registrations with their invoices. If invoiced hours and registered attendance do not match, ask for an explanation before you pay. And if you ever receive a notice, well-kept hours help show how much work was really performed under your contract.
Flanders: duty of care without passport checks
In Flanders, a duty of care has applied in risk sectors since 1 January 2026 to prevent the illegal employment of non-EU nationals. Since 16 October 2026, you as a client no longer need to request the passport or travel document. The explanation does not state which documents are still needed; have this confirmed by your social secretariat or legal adviser.
What should you put in your contract with subcontractors?
The official guidance points to three agreements you should put in writing. Other clauses are possible, but fall outside the scope of this article.
- The registration method. Who provides the registration tool, and how do the data reach the NSSO correctly? For temporary workers, a contractual agreement is even one of the two ways to meet your duty.
- Notice of further subcontracting. The subcontractor informs you in advance, before bringing in subcontractors of its own, so the declaration of works stays complete.
- Termination in case of wage debts. You can escape liability for wage debts by ending the cooperation, but only if the contract provides for that option.
Also plan a fixed check when each subcontractor starts: are they listed in the declaration of works, do they have a Limosa-1 certificate if they come from abroad, and are they free of social security or tax debts? A planning per site helps you keep that overview; read more about planning for construction
How MyVIRO helps
MyVIRO is an employee self-service app that lets your employees check in and out on site and register their hours per site or assignment. Registrations go straight to CIaO through the NSSO web service. The location is only recorded at the moment of checking in or out, never outside working hours.
Per team, you choose which functions are visible, for example only check-in and check-out for a team of temporary workers. In the back office you immediately see missing check-ins, deviating locations and open approvals, before payroll preparation. Validated data flow to your HR, ERP or payroll system, or to VIRO for pre-payroll. MyVIRO does not calculate wages, and the NSSO does not certify software: responsibility stays with you as the employer.
- See how MyVIRO works
- Discover MyVIRO for companies
Request a demo and discover how your teams can check in and out smoothly on every CIaO site from 1 April 2027.
Read also
- Is my construction site subject to CIaO? The 500,000 euro threshold
- CIaO: the app is the easy part. How to get your people to register correctly every day
- Employees' own phone and GPS for time registration: what the GDPR allows
Frequently asked questions about subcontractors and temporary workers under CIaO
No. Everyone registers themselves, in real time, at the workplace. You must, however, make sure that your subcontractors and their employees can register, with a registration system or an agreed alternative.
The company where the temporary worker works. It provides the registration tool or sets out the registration method in a contract with the agency.
Anyone who meets their own obligations is not liable when an employee forgets to register, makes a mistake or refuses. So make sure you can show that registration was possible.
Then you report this electronically through the NSSO service Limosa Notification Duty, before work starts. Your report does not release the foreign employer from its own declaration.
No. The regulation still has to be published in the Official Journal of the EU and most rules only apply two years after entry into force. Until then, the Limosa declaration remains the rule.
For social security debts you withhold 35% of the invoice amount and pay it to the NSSO; for tax debts it is 15%. Check the databases when you sign the contract and during execution.
Yes. Subcontractors without staff must also be included in the declaration of works, and on a CIaO site a self-employed person registers their own presence.
Sources
- NSSO, Check in and out at Work, who must register (in Dutch): socialsecurity.be/check-in-and-out-at-work
- NSSO, Declaration of works, frequently asked questions (in Dutch): socialsecurity.be/ddt
- NSSO, Limosa Notification Duty (in Dutch): socialsecurity.be/meldingsplicht
- FPS Employment, Labour and Social Dialogue, Joint and several liability, general scheme (in Dutch): werk.belgie.be
- kmo.partners, Posting in the EU and Flemish chain liability relaxed, 19 October 2026 (in Dutch): kmo.partners (posting) and kmo.partners (Flanders)
- Council of the EU, agreement on digital posting declarations, 23 June 2026 (German version): consilium.europa.eu
Author: Jean-Philippe Delberghe at MyVIRO. Published on 23 October 2026. Last updated on 23 October 2026.
This article is an informative explanation and not legal advice. Consult your social secretariat for your specific situation.