Deliver results, not people
Supplying personnel is prohibited.
Making personnel available to a third party with employer authority is unlawful in Belgium. The user is liable too.
Article 31 of the Law of 24 July 1987 states something that surprises most business owners: you may not, as a matter of principle, make your personnel available to a third party who exercises over them any part of the authority belonging to an employer. Temporary agency work is the carved-out exception and it is lawful only through an agency holding recognition from the competent Region. Everything else that looks like lending people is prohibited, however informally it came about.
The reason this belongs on a support company's website is that the consequences do not fall only on the supplier. Where personnel have been unlawfully made available, the user can be held jointly and severally liable for social security contributions and remuneration, and an employment contract can be deemed to exist between the user and the worker. A client who asked for someone two days a week, and got them, may be carrying an exposure nobody mentioned at the time.
So the structure of an engagement is not a stylistic preference. We take on defined deliverables and perform them under our own direction and organisation. An interim mandate is written down with its objective, period, authority and reporting line. And where what a business actually needs is workers under its own supervision, the honest answer is a licensed agency rather than a support contract dressed up to look like one. Saying that costs us engagements and is the reason the boundary is worth anything.
Supplying personnel is prohibited.
Objective, period, authority, reporting.
ITAA, the Bar and the FSMA, as applicable.