Royal Mail workers will now stage two x 48-hour strikes in ongoing rows over pay and conditions.
It announced strikes will take place in the run-up to Christmas, including Black Friday on November 25.
The union representing Royal Mail workers – The Communication Workers Union (CWU) – has called the company’s latest pay offer “unacceptable”.
Royal Mail Group said it had put forward a deal on Monday, which included a pay rise worth 7% of a worker’s salary over two years, and a 2% lump sum this year – but the offer was subject to agreeing changes with Sunday working and starting times.
The CWU, which represents around 115,000 workers, previously called off planned walkouts on Sunday.
It has been at loggerheads with Royal Mail over pay failing to keep in line with the cost of living.
An average postal delivery worker earns less than £25,777.
Royal Mail reported losses of £219m in the first half of 2022, which demonstrated something had to change.
Talks between the union and the company have been held at the conciliation service Acas, and planned strikes in the next two weeks were called off following a legal challenge by the company.
The union has withdrawn strikes planned for November 12 and 14, saying it wants to take more “proportionate” action.
The CWU’s postal executive is due to meet n Thursday to discuss new actions in the Christmas build-up, adding that the union will hold a vote to reject Royal Mail’s pay deal and whether workers have confidence in the company’s chief, Simon Thompson.