Vincent Houssin of the liberal public workers union told the VRT: "At the minute there's a staff shortfall of 3,000. Some police zones really have no leeway whatsoever. We won't be able to do the job properly in the long-run."
Extensive checks for people without the right paper work led to 352 people being detained in only two weeks’ time.
Under Mr Jambon's plans the checks are being carried out across the country and include known people-trafficking routes along motorways and motorway car parks, but checks are also being performed at airports and international rail stations.