Where can I find the regulations for the duty to notify?

On wetten.overheid.nl, you can find the available regulations (information in Dutch).

The regulations are included in the Terms of Employment Posted Workers in the European Union Act and the Foreign Nationals (Employment) Act Implementation Decree. For collective agreements, they can be found in the Dutch Collective Agreements Binding and Non-Binding Provisions Act. The terms of employment included in the ‘hard core’ are set out in Dutch labour legislation, i.e. the Minimum Wage and Minimum Holiday Allowance Act, the Working Hours Act, the Working Conditions Act and the Equal Treatment Act.