Dog-owners have been urged to keep their animals under control during the school holidays to tackle the "unacceptably high" number of attacks on postal workers.
The Royal Mail and the Communication Workers Union warned that attacks usually increase in the summer months, placing postmen and women in danger of injury.
There were 3,100 attacks in the year to April, down by 14% on the previous year following a £100,000 awareness campaign by the Royal Mail, which will be stepped up in the autumn in areas including Reading, Huddersfield, North Tyneside and Truro.
Ian Stockdale of the Royal Mail said: "Even just being threatened by an unrestrained pet is a frightening situation for our delivery staff and we would appeal to owners to keep their pets under control."
Dave Joyce of the CWU said: "The age-old image of the dog attacking the postman is not a laughing matter. Thousands of our members are bitten every year and hundreds suffer debilitating injuries which leave them with physical and psychological scarring."