Subcontractors are indispensable in many public contracts — from specialised installers in construction to IT consultants in digital projects. But subcontracting is also one of the most underestimated risk factors. A subcontractor who falls under an exclusion ground, fails to deliver, or is replaced without approval can jeopardise the entire contract.
The basic rule: freedom with disclosure obligation
European and Belgian law do not in principle restrict the use of subcontracting. A tenderer may subcontract the entire work or part of it, unless the specifications explicitly restrict or prohibit this for certain core tasks.
What the law does require is transparency. The tenderer must indicate in the tender which part of the contract it intends to subcontract and who the intended subcontractors are, insofar as they are known at that time.
When must you declare subcontractors?
For contracts above the European threshold, the tenderer is required to indicate in the ESPD whether it will use subcontractors. If the authority requests it in the specifications, the tenderer must also disclose the identity of the proposed subcontractors.
The authority may also require in the specifications that the tenderer states what percentage of the contract will be subcontracted, and for which specific tasks.
Exclusion checks on subcontractors
An important aspect: the authority may (and in certain cases must) check whether the proposed subcontractors fall under a mandatory exclusion ground. Belgian law allows the authority to require the replacement of a subcontractor in an exclusion situation.
In practice, this means the authority may request:
- a criminal record extract from the subcontractor,
- a social security certificate,
- a tax certificate,
- or a declaration that the subcontractor is not in a state of bankruptcy.
The tenderer is therefore well advised to collect these documents in advance — even if the check is not standard for every contract.
Chain liability
The main contractor remains fully liable to the authority at all times for the execution of the contract, including the work of its subcontractors. The fact that a shortcoming was caused by a subcontractor does not release the main contractor from its responsibility.
Direct payment to subcontractors
The Royal Decree on Execution provides for the possibility of direct payment by the authority to the subcontractor, when the main contractor fails to meet its payment obligations. This mechanism protects subcontractors against non-payment by the main contractor.
The Act of 22 December 2023 has further strengthened the position of subcontractors (especially SMEs) with mandatory advance payments and transparency measures.
Changing subcontractors during execution
Replacing a subcontractor during execution is not without risk. The authority may require that any change of subcontractor — particularly if that subcontractor brings specific capabilities for which it was proposed in the tender — be approved in advance.
If the original subcontractor was considered an essential element of the tender (for example because its references contributed to the selection), a replacement may be refused if the new subcontractor does not possess equivalent qualifications.
Procedure for changes
- The contractor notifies the authority in writing of the intended change.
- The authority checks whether the new subcontractor meets the selection criteria and does not fall under an exclusion ground.
- The authority approves or refuses the change with reasons.
Specific rules for construction
Additional rules apply in the Belgian construction sector. Subcontractors performing works requiring contractor qualification must themselves hold the appropriate qualification (correct category and class). The main contractor cannot “lend” its qualification to an unqualified subcontractor.
Regarding social legislation, the chain of subcontracting is particularly relevant: the main contractor can be held jointly liable for wage and social security debts of its subcontractors. The Belgian Act on chain liability (Chapter IV/1 of the Social Security Act) applies here.
Contractual clauses
Experienced contractors include specific clauses in their subcontracting agreements:
Back-to-back clauses. The obligations from the main contract are mirrored to the subcontractor: the same quality requirements, the same penalty clauses, the same deadlines.
Exclusion declaration. The subcontractor declares that it does not fall under an exclusion ground and undertakes to inform the contractor immediately if that changes.
Replacement clause. The contract provides for the possibility of replacing the subcontractor if it underperforms, with a reasonable transition period.
Confidentiality and IP. The subcontractor respects the confidentiality obligations from the main contract and transfers relevant IP rights.