If the non-European worker is an invited professor, the type of authorisation varies based on the duration of the employment in Belgium.
(art. 9,8 royal decree 09/06/1999)
The invited professor will work in Belgium for more than 90 days (and four years at most)Apply for a single permit
The invited professor will work in Belgium for maximum 90 daysApply for a work permit
(In case of successive jobs, the previous periods will be taken into account for the calculation of the 90 days. If the 90 days are exceeded, see the procedure for a single permit.)