Your employer is obliged to check your identification with a valid identification document when you work for the first time for the business.
So are you going to work at a business for the first time? Don't forget to bring a valid identification document. If you already worked for the business before, it is no longer necessary.
Make sure that the identification document contains your Citizen Service Number (BSN) and nationality and therefore a driver's license for example is not a valid identification document.
In addition, your employer is not allowed to make a copy of your identification document, unless you have the nationality of a country outside the European Economic Area.