Royal Mail workers are set to stage two 48-hour strikes around Black Friday and Cyber Monday in a dispute over pay.
The “historic” walkout was announced for November 25 and November 28 by the CWU union in a dispute over pay, jobs and conditions.
However, the union withdrew strikes planned for November 12 and 14, saying it wants to take more “proportionate” action.
The union described an offer made by Royal Mail on Monday as a “surrender document”, saying it involves attacks on terms and conditions as well as redundancies.
The offer will be put to CWU members in a ballot, with the union recommending rejection. Its members are also being asked to vote no confidence in Royal Mail chief executive, Simon Thompson.
The union’s general secretary, Dave Ward, said industrial action will continue in the run up to Christmas unless the dispute is resolved.
A Royal Mail spokesman said: “On Monday October 31, Royal Mail proposed a new pay-for-change offer to the CWU worth 9% over two years, despite making a loss of £219 million in the first half of the year.
“The CWU have been in talks with us at Acas and claim they are open to change but they now need to show it.
“Instead, the CWU have announced four days of strike action which will damage our business further at our busiest time of year.
“The CWU is playing a dangerous game with its members’ jobs and the future of Royal Mail.
“We urge CWU to withdraw these strikes for the good of our customers and our people.
“We apologise to our customers for the inconvenience the CWU’s continued strike action will cause.
“We are doing all we can to minimise delays and keep people, businesses and the country connected."