Most PhD candidates fall under a collective labor agreement (collectieve arbeidsovereenkomst, cao), which describes a large part of their rights. A cao is a contract containing agreements the (representatives of) employees have made with the employer. This includes agreements about wages, working hours, allowances, holidays, training, and pension.
Most PhD candidates fall under three collective agreements:
Be aware that your contract can fall under different conditions than the above. If you want to know your rights, you can consult the four types of PhD candidates (Dutch only), courtesy of the Association of Universities in the Netherlands. You can always ask specific questions regarding your rights to PNN or to your local PhD council.
At the end of 2019 a page will be accessible with extensive information about PhD rights.