Article 7:653a Dutch Civil Code, Book 7

Paragraph 1

A stipulation by which the employer prohibits or restricts the employee from performing work for others outside the times at which the work is to be performed for that employer is void, unless that stipulation can be justified on the basis of an objective reason.

Paragraph 2

The employer may not disadvantage the employee on account of the employee asserting, in or out of court, the rights conferred on him or her by this Article, having provided assistance in that regard or having filed a complaint about it.