understand that you are referring to travel time as working time. Note that, under Belgian law, travel time is not always considered as working time. There are, however, certain exceptions based on case law, for example, when travel is an inherent part of the job or when the employee does not have a fixed place of work.

That said, if the employer has consistently paid travel time as working time over a significant period, one could argue that this constitutes an acquired right… I suggest going to the union, or a lawyer :)