Royal Mail has said it would be “materially loss making” in the UK if planned strikes by 115,000 workers go ahead.
In a post on Twitter on Tuesday, the Communication Workers Union (CWU) said that workers will stage a walkout on August 26, August 31, September 8 and September 9.
The CWU said it will be the biggest strike of the summer so far to demand a “dignified, proper pay rise”.
It follows a recent ballot for strike action, which saw members vote by 97.6 per cent on a 77 per cent turnout to take action.
Shares in the privatised business fell more than two per cent in early trading on Wednesday.
In a statement Royal Mail said: “This decision by the CWU is an abdication of responsibility for the long-term job security of its members. In more than three months of talks, CWU has failed to engage meaningfully on the business changes required.
“The negative commercial impact of any strike action will only make pay rises less affordable and could put jobs at risk. The CWU has a responsibility to recognise the reality of the situation Royal Mail faces as a business, and to engage urgently on the changes required.
“Royal Mail remains ready to talk with the CWU to try and avert damaging industrial action and prevent significant inconvenience for customers. But any talks must be about both change and pay.
“Royal Mail has contingency plans in place and will be working hard to minimise disruption and restore normal service as soon as possible.”
CWU general secretary Dave Ward said on Tuesday: "Nobody takes the decision to strike lightly, but postal workers are being pushed to the brink.
"There can be no doubt that postal workers are completely united in their determination to secure the dignified, proper pay rise they deserve.
"We can't keep on living in a country where bosses rake in billions in profit while their employees are forced to use food banks.
"When Royal Mail bosses are raking in £758 million in profit and shareholders pocketing £400 million, our members won't accept pleads of poverty from the company.”
CWU deputy general secretary Terry Pullinger said: “Our members know full well what they are worth.
"They are willing to fight for a no-strings, real-terms pay rise that they are fully entitled to.”
But Royal Mail’s operations director claimed the CWU “failed to engage in any meaningful discussion on the changes we need to modernise”.
Ricky McAulay said: “The CWU rejected our offer worth up to 5.5 per cent for CWU grade colleagues, the biggest increase we have offered for many years. In a business that is currently losing £1 million a day, we can only fund this offer by agreeing the changes that will pay for it,” he explained.
“Royal Mail can have a bright future, but we can’t achieve that by living in the past. By modernising we can offer more of what our customers want at a price they are willing to pay, all whilst protecting jobs on the best terms and conditions in our industry.
“We apologise to our customers for the disruption that CWU’s industrial action will cause. We are ready to talk further with CWU to try and avert damaging industrial action but, as we have consistently said, it must be about both change and pay.”
The CWU has informed us that their members will undertake strike action on 26 and 31 August and 8 and 9 September. We're ready to talk further with the CWU to try to avert industrial action. Contingency plans are in place. You can still send your items: https://t.co/3NUFqEFN8l
— Royal Mail (@RoyalMail) August 9, 2022
Customers are advised to post items as early as possible prior to the planned strikes. It warned that collections “will be less frequent” on strike days and advised people to check online for updates.
Royal Mail said on days when strike action is taking place, it will “deliver as many Special Delivery and Tracked24 parcels as possible”, prioritise the delivery of Covid-19 test kits and medical prescriptions “wherever possible”, and suspend the delivery of letters, with the exception of Special Delivery.