I see and it's interesting to see how it works elsewhere.
I think collective labor agreements regulate it in many fields over here. And if it has been registered in an agreement like that and the field has agreed the agreement, employees have to get their 4 weeks vacation. I've caught that many fields have a clause like that in their agreement. At least many of people I know have a vacation like that (=very probably they've an agreement like that).
I've also caught that you can agree that you divide your vacation in smaller pieces but many take whole the month at once.