All things considered, providing the legal basis or authority for sending a notice is pertinent 
As I have noticed this helps to ensure the legitimacy of your notice. To do so you may include,
  • a contractual clause
  • a legal obligation
  • or a specific law or regulation supporting the notice.
By doing so and by citing this basis or authority, the recipient of the notice will have a clear understanding of why it is being sent and its legal standing.