Changes to withholding obligation as of 1 May 2026

For a long time, Belgian legislation has included a liability regime for the contracting of works in immovable property: any client or contractor who calls on a (sub)contractor for the execution of works in immovable property is jointly and severally liable for the social security and/or tax debts that this (sub)contractor has at the time of concluding the building contract and at each payment of an invoice. However, provided that the invoices of the co-contracting party with social and/or tax debts are correctly withheld and paid to the NSSO and the tax authorities, the client or contractor is released from this joint and several liability. From 1 May 2026, a fundamental change to this withholding obligation will come into effect. The new rules extend the existing mechanism while introducing an important restriction.

Works in immovable state

The existing regulations on the withholding obligation and joint and several liability relate to works in immovable state, the supply of ready-mixed concrete, works that fall under the Joint Committee for Security and/or Surveillance Services, and works in the meat sector.

Works in immovable state include, in essence, all works relating to a property by its nature. This covers a wide range of activities, including the construction, remodelling, finishing, furnishing, repair, maintenance, cleaning and demolition of buildings or other immovable structures, including the supply and immediate installation of movable property that makes them immovable by nature (e.g. fitted kitchen). It also includes the attachment to a building of, i.a. heating, ventilation, sanitary or electrical installations, as well as the supply and/or installation of wall coverings or floor coverings. A number of activities from agriculture, horticulture and forestry are explicitly excluded from the scope.

Belgium tightens control on social debts

The withholding obligation for social and tax debts is not a new obligation. For some time now, clients and contractors have been obliged to withhold part of an invoice if their (sub)contractor has social or tax debts, if they want to free themselves from their joint and several liability for these debts of their (sub)contractor.

Before paying an invoice for the works targeted, you must  check whether the withholding obligation applies via checkinhoudingsplicht.be or for foreign companies and self-employed persons via A1, PDOK (in case of construction) and a tax certificate.

If the contractor or subcontractor has social debts, you must withhold 35% of the amount you owe them (excluding VAT) and pay it to the National Social Security Office. If the contractor also has tax debts, you must withhold (a maximum) of 15% of the amount you owe them (excluding VAT) and pay it to the FPS Finance.

This system is now being further expanded. The new regulations stipulate that from 1 May 2026, social debts must also be taken into account for parties holding the self-employed status. If a (sub)contractor has such debts, 15% of the invoice amount (excluding VAT) must be withheld and transferred to the NISSE.

Until now, the focus has mainly been on employers’ social debts. As a result of this expansion, independent entrepreneurs in the construction chain are now also explicitly subject to control. In concrete terms, this means that independent contractors or directors with overdue contributions can also have an impact on the payment obligations of their clients.  

Limitation: deductions may together amount to a maximum of 50%

Along with this expansion, the law also introduces an important boundary. When both social and tax debts are present, the total deduction from an invoice may not exceed 50% of the invoice amount (excluding VAT). This means that the new withholding obligation for parties holding the self-employed status does not apply if there is already a withholding obligation for both the FPS Finance (15%) and the NSSO (35%).

Digital tools such as checkinhoudingsplicht.be will automatically take this limit into account when calculating deductions from 1 May 2026.

Strict sanctions for those who forget to withhold

Even apart from the joint and several liability for the social and tax debts of the (sub)contractor, the withholding obligation is not a non-binding formality. If a client, contractor or subcontractor fails to carry out the new mandatory withholding, an administrative fine of 15% of the invoice amount (excl. VAT) can be imposed, with a maximum of EUR 10,578.23 (2026). For the already existing withholding obligation for the benefit of the NSSO and FPS Finance, it is an administrative fine equal to twice the amount that should have been withheld and paid.

Moreover, this can also make a company show up as “not in order” in the official control systems that companies use to screen partners.

Looking ahead

In addition to these far-reaching changes from 1 May 2026, there are also a number of NSSO innovations in the pipeline for 2027. The classic Declaration of Works (30bis) is evolving into CATENA with a modern, future-oriented architecture, new functionalities, improved export options and only secure access. In addition, CIAW will also be extended to CIAO for real estate works – previously this was only done in the cleaning sector, where employees have to register not only a checkin, but also a checkout on site and in real time.

Curious about the impact of the above changes on you and how you can prepare for this as a self-employed person?

Feel free to contact us, our specialists will guide you through the process.