NSSO Attendance Declarations in Belgium Explained: Checkinatwork, CIAO and Dimona

The Belgian National Social Security Office (NSSO/RSZ/ONSS) requires attendance declarations for three specific sectors: construction, cleaning, and meat processing. As an employer in one of these sectors, it is critical to understand which NSSO declaration obligation applies to you. Affected Sectors and Their Declaration Systems Construction Sector Belgium (NACE 41-43) Obligation: Checkinatwork attendance registration Since: 2014 Deadline: Check-in before work begins Responsible party: Every employer/self-employed person on the site Cleaning Sector Obligation: CIAO declaration (Check In And Out) Since: 2016 Deadline: Check-in at start, check-out at end Responsible party: The cleaning employer Meat Processing Obligation: CIAO declaration Since: 2019 Deadline: Real-time registration Responsible party: The meat processing company Dimona Declaration: The Foundation for All Sectors Beyond Checkinatwork and CIAO, the Dimona declaration is mandatory for ALL Belgian employers. Dimona (Declaration Immediate/Onmiddellijke Aangifte) registers the start and end of every employment relationship: - Dimona IN: Must be submitted before the first working day - Dimona OUT: Must be submitted at the end of the employment relationship In the construction sector Belgium, there are additional Dimona requirements for foreign workers (Limosa declaration, A1 certificate). NSSO Penalties for Non-Compliance The NSSO actively monitors attendance registration compliance through Social Inspection officers. Penalties are: - Administrative sanctions: €50 to €2,500 per violation - Social corrections: €6,000 per unregistered worker found during labour inspection - Criminal prosecution for systematic violations Required Data in an NSSO Attendance Declaration Every attendance declaration must include: - NISS/INSZ number of the worker (mandatory) - Date and time of arrival - Date and time of departure (CIAO) - Identification of the workplace/construction site - Limosa reference for foreign workers Integration with Checkin OK Checkin OK processes all three declaration types — Checkinatwork, CIAO declaration, and Dimona status check — from a single upload. Our platform validates NISS/BIS numbers via modulo-97 checksum and generates NSSO XSD v1.13-compliant XML. See also our guide on Automating CIAO Declarations. Frequently Asked Questions about NSSO Declarations Q: Does the attendance registration obligation also apply to self-employed workers in the construction sector? A: Yes. Self-employed subcontractors active on Belgian construction sites are also required to register via Checkinatwork, regardless of their status. Q: What is the difference between an NSSO declaration and a Dimona declaration? A: Dimona registers the employment relationship (start/end of contract); Checkinatwork/CIAO register daily attendance at the workplace. Both obligations exist independently of each other. Q: How long must I keep attendance data? A: NSSO regulations require retention of all attendance data for at least 5 years. Try Checkin OK free — one platform for all your Checkinatwork, CIAO, and Dimona compliance.