An employee reports long-term sick leave, but you see them on social media actively working in the garden or running a side business. Can you check on that? And how far can you go without violating privacy laws? In Belgium, monitoring sick leave is subject to strict rules. This guide explains what is legally allowed, which steps you can take yourself, and when it is better to hire a private investigator. We work from the Antwerp region, strictly within the Private Investigation Act of 18 May 2024.

What does Belgian law say about monitoring sick leave?

In Belgium, monitoring sick leave is legally regulated through the Employment Contracts Act and the Well-being at Work Act. An employer may appoint a company doctor to verify the incapacity for work. That doctor may only share medical data relevant to the return to work, not the diagnosis itself.

In addition, privacy legislation (GDPR) applies. An employer may not carry out covert surveillance, may not place GPS trackers on company cars without clear rules, and may not request access to private social media accounts. Anyone who does so risks severe sanctions and the evidence may be rejected in court.

A private investigator may carry out surveillance, but only within the Private Investigation Act. That law requires prior notification to the FPS Interior and a legitimate assignment. The investigator may not infringe on the privacy of third parties and may not collect information that is not relevant to the investigation.

Which checks can you carry out yourself as an employer?

You may call in a company doctor. That is the most direct and legally safe step. The doctor assesses whether the employee is actually unfit for work and can propose a date for returning to work.

You may consult public information. If an employee publicly posts about activities that do not match the reported condition, you may take note of that. However, you may not use that information as the sole evidence without a proper procedure.

You may not hire a private investigator without a legitimate reason. An investigator may only be called in if there is a suspicion of fraud and if the company doctor does not provide a clear answer. The assignment must be reported to the authorities and the investigator must comply with the code of ethics.

When is a private investigator allowed in cases of sick leave?

A private investigator is allowed when there is a concrete suspicion of abuse. Think of an employee who has been at home for months with back problems, but regularly does heavy jobs for friends or runs their own business. The investigator can then carry out surveillance on public roads or in places that are freely accessible.

The investigator may not take images inside the private home, may not tap phone calls, and may not assume a false identity. All findings are recorded in a report that can serve as evidence before the labour court, provided the investigation was conducted lawfully.

In the Antwerp region, we often work for SMEs and larger companies that want to confirm or refute a suspicion of fraud. Our reports are detailed, dated, and compliant with the Private Investigation Act. You get direct contact with the manager who personally follows up on the file.

What may a private investigator not do during a sick leave check?

A private investigator may not infringe on the privacy of the employee or their family. They may not film inside the home, open mail, request bank details, or obtain medical information. They also may not contact the treating physician or the health insurance fund.

The investigator may not exert pressure on the employee or their environment. They may not approach witnesses in a way that could be seen as intimidation. All actions must be proportionate and necessary for the investigation.

If these rules are violated, the evidence becomes unusable and the investigator may face criminal prosecution. That is why it is essential to work with a recognised agency that strictly complies with the Private Investigation Act. At Amberes Investigations, legality always comes first, without exception.

How does a sick leave investigation work in practice?

The investigation starts with an intake interview. You explain the situation and we assess whether there is a legitimate basis for surveillance. We then draw up an investigation plan, with clear agreements on duration, location, and reporting.

During the surveillance, we record factual findings: times, places, activities. We do not make interpretations, only objective observations. These are compiled in a report with photos or video material, insofar as legally permitted.

Afterwards, we provide you with the report and discuss the next steps. You can use the report in proceedings before the labour court or in a dismissal for serious cause. We advise you on the legal value and the risks, but the decision lies with you or your lawyer.

Common mistakes when monitoring sick leave

A common mistake is carrying out surveillance yourself. An employer who drives past the home of a sick employee in the evening is on thin ice. Those findings are rarely accepted by the court and can lead to a complaint for stalking.

Using social media without context is also risky. A photo of an employee at a restaurant does not mean they are not unfit for work. Context is crucial: is it a one-off activity or a pattern that contradicts the diagnosis?

Finally, ignoring the procedure is a frequent problem. Anyone who hires an investigator without a legitimate reason or without the mandatory notification not only loses the evidence, but may also be held liable themselves. Therefore, always seek assistance from a professional who knows the rules.

What legal basis makes monitoring possible?

An employer cannot simply hire a detective on a whim. The purpose must be legitimate, the monitoring proportionate, and there must first be a concrete suspicion of abuse. The company doctor remains the first instrument. Only when their findings raise questions about actual behaviour, such as a side job or heavy manual work, does a private detective come into the picture.

The assignment falls under the Act of 2 October 2017 regulating private and special security. The agency must hold a licence from the FPS Home Affairs. Every assignment is registered. If a detective gathers evidence without a licence, that evidence may be excluded in later proceedings.

Where does the right to monitor end?

The private home, the garden behind a high hedge and shielded social media remain out of reach. Surveillance is only allowed in places where the employee appears in public. A public car park, a DIY store or a sports club are permitted. As soon as the detective enters a home or films through a window, they are acting unlawfully.

The employee's privacy carries significant weight. For a short absence, prolonged surveillance is disproportionate. The employer must choose the least intrusive means that can confirm or refute the suspicion.