Employment Act (Chapter 91): While appreciation letters are not specifically regulated, any references to the employment relationship should align with Singapore's employment laws. This forms the basic framework for any employer-employee documentation.

Personal Data Protection Act (PDPA): Governs the collection, use, and disclosure of personal data. When drafting the appreciation letter, ensure any personal information included complies with PDPA requirements and data protection principles.

Prevention of Harassment Act (POHA): Ensures that the content of the letter remains professional and free from any statements that could be interpreted as harassment or inappropriate behavior. The letter should maintain a respectful and professional tone.

Defamation Laws: Requires careful consideration to avoid any potentially defamatory statements. The letter should stick to factual and positive statements about the intern's performance and contributions.

Company Policies: Internal guidelines and protocols that govern how company documentation should be handled and what content can be included in official communications.

Industry Regulations: Specific regulations that may apply depending on the industry sector (e.g., financial services, healthcare) which could affect the content and handling of official documentation.

Professional Standards: Best practices and professional norms for business communication that should be followed when drafting formal appreciation letters to maintain professional credibility.