Staff are obliged to report ancillary activities. You are not permitted to carry out ancillary activities unless you have the approval of the Board of your faculty or service. Even if you do not carry out ancillary activities in the sense of these regulations, you are still required to report this.
Leiden University Framework Regulation on Ancillary activities
For reporting ancillary activities, or changes in your ancillary activities you can use Self Service. If you don’t have excess to Self Service you can contact your HR department.