Which travel documents do posted workers need?

The workers you post must have a travel document.

Your workers must have a travel document. For residents of the EU, EEA or Switzerland, a national passport or ID will suffice. In addition to their national passport, workers from outside the EU, EEA or Switzerland must have a residence permit and a work permit for the country where they usually work (EU member state, EEA member state or Switzerland), which are valid for at least the entire duration of their posting to the Netherlands. You can find more information about workers from outside the EU, EEA or Switzerland here.