The 8 most common mistakes when registering temporary workers

Registering and onboarding temporary workers, agency staff, student workers or flexi-jobbers, looks simple enough. On paper. In practice, employers keep tripping over the same pitfalls: a forgotten Dimona (immediate employment declaration), vague arrangements or a sloppy handover that ends in legal risk, friction in the workplace or double work for HR.

The good news? Most of these mistakes are easy to avoid, once you know where things tend to go wrong. Onboarding is more than letting someone start: it is how a new hire feels welcome, understands their role and can genuinely contribute to the team.

In this article, we map out the 8 most common mistakes when onboarding agency workers and new hires. You will see not just which stumbling blocks come up most often, but above all how to sidestep them yourself: through clear arrangements, better preparation and a professional onboarding process.

1# No signed contract before day one

One of the most common mistakes when onboarding a new employee, especially in agency work or temporary employment, is not having a signed employment contract before the first working day. In Belgium this is mandatory: without a valid student contract, temp agency contract or other employment contract, the worker is automatically regarded as an ordinary employee under full NSSO (National Social Security Office) status.

The fallout can be serious, both when the working relationship ends and during an inspection. Without a contract signed in advance, any dispute over work schedules, pay or the length of the assignment is settled against the employer. The risk of fines, reclassification and retroactive contributions is very real.

Solution:
Draw up the employment contract well in advance and make sure it is signed before work begins. For ordinary employers, digital signing runs through recognised methods such as itsme or eID, because simple signatures are not legally valid.
As a temp agency, we have more flexibility here: we are allowed to use simplified digital signatures, which are legally recognised within the rules of temporary agency work.

That way, every worker starts correctly, on solid legal ground and without uncertainty.

2# Choosing the wrong contract type

A common onboarding mistake is choosing the wrong contract type: not every kind of temporary work can sit under a day contract. In Belgium, day contracts may in practice be used almost exclusively through a recognised temp agency.

Even for student work, day contracts are in principle only allowed through temporary agency work. Direct day contracts between employer and worker are permitted only in exceptional cases and must always be objectively justifiable (for example, highly unpredictable assignments).

When there is a continuous or structural schedule, a weekly, biweekly or monthly contract is mandatory. Using day contracts without a valid reason can lead to remarks from the Supervision of Social Laws (the labour inspectorate) and possible penalties.

Solution:
Always match the contract type to the reality of the work. Use day contracts only when the conditions for temporary agency work or the exception criteria are met. For longer or predictable assignments, a weekly or monthly contract is the better choice. That way the employment stays legally correct and you steer clear of problems during inspections.

3# Forgetting the Dimona or filing it late

One of the most common onboarding mistakes in temporary employment is filing the Dimona declaration too late, or not at all. This notification to the NSSO is mandatory before the student worker, agency worker or other temporary worker starts work. Without a valid Dimona, the person is officially not registered as an employee, which carries serious consequences in the event of an occupational accident or inspection.

Late or incorrect Dimonas can lead to administrative fines, reclassification of the status and loss of reduced social security contributions. On top of that, the employer looks negligent in employing students or agency workers, which can sour the relationship with the inspection services.

Solution:
Automate the Dimona through a payroll or HR system so that every registration happens on time and with the correct status. That way you avoid mistakes, protect the new worker and keep your organisation fully compliant with the law.

4# Applying the wrong pay in temporary employment

A common mistake when onboarding temporary workers is applying the wrong pay. Agency workers, student workers and other temporary staff are entitled to the sectoral salary scale that applies within the Joint Committee (JC). Their pay must line up with that of other workers in the same role, including any benefits such as meal vouchers or bonuses.

Underpaying a student worker or agency worker risks not only recalculations by the NSSO, but also friction within the team. A miscalculated wage can also trigger inspections or obligations to pay arrears.

Consequence:
Incorrect pay can be corrected retroactively, often with additional contributions and administrative costs.

Solution:
Check the Joint Committee's salary scale in advance and apply pay correctly, even for short assignments. Preferably use a payroll system that automatically assigns the right sector information and benefits.

5# Missing mandatory documents

Another common mistake when onboarding temporary workers is forgetting mandatory documents. Beyond the employment contract, several legal requirements have to be in order before work begins: valid occupational accident insurance, registration in the personnel register and, in some sectors, a certificate of medical fitness.

When these documents are missing, the worker is not fully protected and the employer is exposed during an inspection or accident. For agency work, student work or seasonal work in particular, the social inspectorate applies these checks more strictly.

Solution:
Work with a fixed checklist or use a digital platform that automatically reminds you of missing documents. That way the onboarding of new employees runs in a legally correct and administratively complete manner.

6# No new Dimona when a contract is extended

One of the most underestimated mistakes when employing temporary workers is forgetting a new Dimona when a contract is extended. When an assignment runs on, or a student, agency worker or temporary worker stays longer than originally planned, a new Dimona declaration must be filed with the correct start date.

If this is skipped, the worker is officially considered undeclared, which can carry heavy legal consequences. In the event of an occupational accident, the employer can even be held fully liable, because there is no valid registration in place.

Risk:
Inspection services can impose fines running into thousands of euros, on top of possible regularisations of social security contributions.

Solution:
Register every extension immediately through a new Dimona, or work with a payroll system that automatically sends a reminder when a contract is about to end. That way the employment stays correctly covered, without administrative surprises.

7# Ending a contract the wrong way

A common mistake in temporary employment is assuming a contract can simply be stopped before its end date. It cannot. When an employment contract is terminated early, or when the working relationship stops unexpectedly, specific rules apply, depending on the contract type (agency work, student contract or fixed-term employment contract).

Get the termination wrong and you risk conflicts over notice periods, pay rights or even damages. In certain cases, a student worker or new employee is entitled to notice, especially when the agreement has already been running for some time. Without correct application, the employer can be held liable.

Solution:
Inform yourself in advance about the conditions for ending an agreement, or work with an HR or payroll partner who follows this up automatically. That way you prevent disputes and guarantee a legally correct end to the employment.

8# Ignoring the rules for students and flexi-jobbers

Students and flexi-jobbers fall under a different status than ordinary employees and are bound by specific legal limits. For student work, a quota of 650 hours per year applies, during which the student works at reduced social security contributions. If this limit is exceeded, the full benefit lapses and the work is subject to the ordinary NSSO rates.

There are clear limits for flexi-jobbers too. They must work at least 4/5 as their main occupation (or be in an equivalent situation, such as retirement), otherwise the flexi-job loses its favourable tax and social security regime. If the conditions are not met correctly, the employment can be reclassified, resulting in unexpected contributions and corrections.

Consequence:
If hours are exceeded or the status is wrong, contributions can suddenly rise considerably. Employers risk retroactive regularisations, backdated social security contributions and, in some cases, even financial penalties.

Solution:
Monitor the status of every student worker or flexi closely through Student@work or through mycareer.be. A correct estimate of hours and status prevents benefits from being lost.

Bonus Tip 1: Showing up is not the same as being ready

One of the most common mistakes is thinking onboarding stops the moment the new worker shows up in the workplace. In reality, the real induction only begins after the first hello. New employees often feel lost when they get no handbook, no structure, no preboarding information. Without clear explanations, fresh information or regular check-ins, an agency worker or new colleague is only physically present, not prepared to add value on their own.

Poor onboarding breeds frustration on both sides. New colleagues do not know when they are meant to work or who to turn to, while the team loses time improvising. The difference between success and failure often comes down to simple follow-up: set clear arrangements, build in moments to gather feedback, and make sure someone owns getting new workers up to speed.

A structured onboarding does not have to be complex. A short handbook, a fixed point of contact and a first day with guidance are enough to build relationships and strengthen the candidate's engagement. That way you avoid onboarding ending in one of the most common mistakes: registering someone, but never really letting them start.

Bonus Tip 2: The wrong hire, no fit or initiative

Many problems during employment start earlier, in recruitment. When someone is hired on the strength of connections, or with favouritism winning out over objectivity, the odds of a genuine fit drop sharply. The right interim professional can make all the difference, but only when the selection rests on measurable criteria: the candidate's flexibility, their self-starting ability and their willingness to be the difference between real team support and wasted time.

Ask for references who can speak to work attitude, and use interview scorecards to gather objective feedback. Interim professionals are often brought in to make a quick impact, but not everyone has the self-starting ability to add value on their own. Finding the right temporary worker takes more than CV screening: involve several team members, ask about engagement and set clear arrangements around availability.

External partners can help you save time and money, as long as quality stays in focus. When recruitment chases the short term instead of long-term employability, you miss the candidate who could really make a difference. The right interim professional knows exactly why they have been brought in, and delivers from day one.

Getting everything right? It can actually be simple

Most mistakes during onboarding do not stem from unwillingness, but from a lack of overview or manual administration. Keeping track of contracts, Dimona, sector salary scales and documents takes precision, and that is exactly where things often go wrong. With the right support, that does not have to be a risk.

Recruit makes temporary employment administratively flawless and legally correct.
Our software guides every step of the process, so you never overlook a single obligation.

What Recruit automates for you:

• Automatically correct contracts and student contracts
• Timely and flawless Dimona declarations with the correct status
• Application of sector salary scales without manual calculation
• Central and secure storage of all documents
• Alerts for extensions or missing data

Result: no risks, no fines, no duplicate work, just certainty and simplicity.

Registering temporary staff without worries?
Discover how Recruit fully streamlines your onboarding process.