What the rules actually ask
In the United States, the Federal Trade Commission's Guides Concerning the Use of Endorsements and Testimonials in Advertising (16 CFR Part 255), revised in 2023, require that any "material connection" between you and a seller be disclosed clearly and conspicuously. An affiliate commission is a material connection. The FTC's plain-English guide, Disclosures 101 for Social Media Influencers, adds that the disclosure must be hard to miss and placed where readers will see it before they act.
In the United Kingdom, the CAP Code enforced by the Advertising Standards Authority requires marketing communications to be "obviously identifiable". The ASA and the Competition and Markets Authority jointly publish the Influencers' guide to making clear that ads are ads, which covers affiliate links directly. Under the Digital Markets, Competition and Consumers Act 2024, the CMA can now fine businesses directly for consumer-law breaches. Across the EU, the Unfair Commercial Practices Directive treats hidden advertising as misleading.
Platforms add their own layer. Amazon's Associates Program Operating Agreement requires the statement "As an Amazon Associate I earn from qualifying purchases" or similar. Google asks that paid links carry rel="sponsored", introduced in 2019, so that they do not pass ranking credit.
The common thread: tell people before they click, in words they understand, every time. A single line in your footer or a separate "disclosure policy" page is not enough on its own.
