Roger Annies, who works at the Barry Delivery Office, created and distributed leaflets that told customers how to opt out of Royal Mail's door-drop service.
The leaflet told recipients that Royal Mail plans to increase the amount of promotional mail it distributes. It also advised them to complete a slip and send it to the Royal Mail delivery office to stop such mail being delivered to their home.
In July, Royal Mail struck a deal with the Communication Workers Union to give post workers a 3.9% pay increase in exchange for revising the limits on the amount of unaddressed mail they carry.
While other types of mail delivery fell last year, unaddressed door-to-door mail deliveries grew by more than 12% to about 3.3bn items.
More than 2.8m people are currently signed up to the Mail Preference Service.