Yes there is a law protection posted workers. Read more about the law in Dutch. Or download the pdf below.
Wet Arbeidsvoorwaarden Gedetacheerde werknemers in de Europese Unie (WagweEU) in Dutch.
A “posted worker” is an employee who is sent by his employer to carry out a service in another EU Member State on a temporary basis, in the context of a contract of services, an intra-group posting or a hiring out through a temporary agency. Read more about posted workers here.
Read more about the difference between a posted worker and direct employment on this page.