For persons from outside the EU: sex work is the only type of work where it is not possible to obtain a work permit (WAV: Wet Arbeid Vreemdeling). The procedure/logical framework of this exception in the labour law for foreigners/law on foreigners is as follows: as soon as a (non-EU) person intends to exercise work for a third person, the employer has to apply for a work permit. Given that prostitution is a legal work, applying for work permit should be possible, but is by definition not possible because the law specifies that for activities that are bound to offering sexual services (including erotic shows) for and with third parties it cannot be applied for a work permit. This prohibition dates from the times before the legalisation of prostitution where the law stated that it was not possible to obtain a work permit for an activity that was not legal.
As far as self-employed/entrepreneurs (in prostitution) concerns: according to the law they are not obliged to apply for the work permit because the above mentioned law concerns only the persons who work for the third parties. So in principle they should be able to establish themselves as self employed sex workers and to receive a residence permit as a consequence. However, the authorities refuse to give this group a residence permit for the purpose of work as self employed in prostitution giving a reason that they do not serve any Dutch interests. The additional argument comes from the ministry of Economic Affaires: they do not perceive sex workers as independent workers and sex work not as economic activity that has economic importance.