Article 30bis explained: withholding obligation and joint liability

Article 30bis of the Belgian law of 27 June 1969 is the legal basis of the withholding obligation. It sets out who must check, what happens if you do not, and why a skipped check can cost you the full invoice amount. Below is the rule in plain language, with the percentages and the cap as they apply in 2026.

What does article 30bis actually say?

Article 30bis provides that anyone who has works carried out by a contractor is jointly liable for that contractor''s social security debts towards the NSSO. To avoid that liability, you must check at every payment whether the contractor has debts at that moment. If so, you withhold a statutory percentage and pay it directly to the NSSO.

The logic is preventive. The legislator wants to avoid works being passed on to contractors who do not pay their contributions. By placing the check with the payer, the entire chain stays financially sound.

Article 30bis has a tax counterpart: articles 400 and following of the Income Tax Code, known in practice as the tax withholding obligation towards FPS Finance. Both checks happen at the same moment, for the same invoice.

Who has the withholding obligation?

You have the obligation as soon as three conditions are met:

1. You pay, in full or in part, an invoice to a contractor or subcontractor.
2. The invoice concerns works covered by article 30bis or 30ter.
3. The payment is made in the course of your professional activity. A purely private order by an individual falls outside the scheme.

It does not matter whether it is an advance, an interim statement or a final settlement: every payment is a separate check moment. If you are a subcontractor yourself, the obligation applies in the opposite direction to the party paying you. In a chain with three or four levels, a check is therefore required at every level.

More examples are in our complete guide to the withholding obligation.

Article 30bis versus article 30ter

Many companies assume the rule only applies to construction. It does not:

• Article 30bis covers classic immovable works: construction and real estate, from new build and renovation to demolition, installations and the supply of ready-mixed concrete with placement.
• Article 30ter extends the scheme to three further sectors: cleaning, meat and security.

The obligations are identical in both cases: check before every payment, withhold when there are debts, keep the evidence. Only the list of activities differs. A full overview per sector is on our sector pages.

The percentages: 35% NSSO and 15% FPS

The percentages are set by law and calculated on the invoice amount excluding VAT:

• 35% when the contractor has social security debts with the NSSO.
• 15% when the contractor has tax debts with FPS Finance.

You do not keep that amount: you transfer it to the authority concerned, with the correct structured reference. The balance goes to the contractor.

The 50% cap

If a contractor has debts with both the NSSO and FPS Finance, the sum would be 50%. The law therefore caps the total withholding at 50% of the invoice amount excluding VAT. In practice you first calculate the NSSO share, then the FPS share, and cap the total at half the invoice.

Checkplicht performs this calculation automatically and shows the NSSO amount, the FPS amount and the capped total side by side, so your bookkeeping can split the payment correctly.

When to check? Before every payment

This is the most common mistake. A check is valid at the moment of payment, not for the duration of a project or a calendar year. A contractor who is debt-free today can be in arrears three weeks later.

In practice:

• Check when each invoice arrives, so you have time to split the payment correctly.
• Check again if time passes between approval and the actual payment.
• Schedule periodic re-checks for contractors you work with on an ongoing basis.

To quickly verify a single company number, use our check withholding obligation page.

Which evidence must you keep?

During an inspection you must be able to show that you checked at the moment of each payment. So keep, per payment:

• the contractor''s company number and its name at that time;
• the date and time of the check;
• the result for the NSSO and for FPS Finance;
• the calculated withholding amount, even when it is zero;
• the proof of transfer to the NSSO or FPS, if an amount was withheld.

Checkplicht stores this automatically and generates, per check, a certificate with a unique ID and QR verification so that an inspector can verify its authenticity.

Joint liability in practice

The sanction is twofold, and that is often underestimated:

• Joint liability for your contractor''s outstanding debts, up to the full invoice amount excluding VAT.
• On top of that, an administrative fine equal to the amount you should have withheld.

For an unchecked invoice of 100,000 euro the worst case reaches 150,000 euro: 100,000 euro liability plus a 50,000 euro fine. The cost of doing the check properly is nowhere near that.

Automating the check with Checkplicht

Checkplicht queries the official NSSO and FPS Finance sources live, calculates the withholding amount including the 50% cap, and archives the evidence next to your supplier. You get an alert as soon as a withholding is detected for one of your contractors, and you choose the cadence of the automatic re-checks yourself.

See the pricing or create an account and try it free for seven days.

Frequently asked questions

When do you have the withholding obligation? As soon as you pay, in the course of your professional activity, an invoice to a contractor for works covered by article 30bis or 30ter. The obligation applies per payment, not per project.

What is a withholding party? The party paying the invoice: the client or the main contractor. That party must check and, where needed, withhold and transfer.

Does article 30bis apply to deliveries? A pure supply of goods without placement is not covered. If the supply is combined with placement or assembly, it is an immovable work and the obligation applies.

How much must be withheld? 35% for social security debts, 15% for tax debts, with a combined cap of 50% of the invoice amount excluding VAT.

How long must the evidence be kept? Allow a retention period that covers the possible inspection window. An inspection can look back several years, so archive the certificate together with the invoice.