The Communication Workers Union (CWU) said workers would walk out on 26 and 31 August and 8 and 9 September. The union described the action as the “biggest strike of summer”.

The decision follows the union’s recent ballot for strike action, which saw CWU members vote by 97.6% on a 77% turnout to take action. This was the biggest mandate for strike action reached since the implementation of the 2016 Trade Union Act.

CWU is demanding that Royal Mail Group make an “adequate pay award” that covers the current cost of living increases for its members.

The union accused Royal Mail management of imposing a 2% pay rise on its employees through executive action, pointing out that those same employees were given key worker status at the height of the Covid-19 pandemic.

CWU said that in an economic climate where inflation has soared to 11.7%, the imposition would lead to “a dramatic reduction in workers’ living standards”.

CWU general secretary Dave Ward said: “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 £758m in profit and shareholders pocketing in excess of £400m, our members won’t accept pleads of poverty from the company.

“Postal workers won’t meekly accept their living standards being hammered by greedy business leaders who are completely out of touch with modern Britain. They are sick of corporate failure getting rewarded again and again.

“The CWU’s message to Royal Mail’s leadership is simple – there will be serious disruption until you get real on pay.”

Royal Mail said it believes there are no grounds for industrial action and said it is ready to talk further with the CWU to try to avert industrial action.

Royal Mail said in a statement: “We have contingency plans in place, and will be working hard to minimise disruption and get our services back to normal as soon as we can to keep people, businesses and the country connected. Meanwhile you can continue to send your parcels and letters and we would encourage you to post early in advance of these dates.”

Royal Mail is currently being investigated by the communication regulator over its failure to meet delivery targets for first class and second class post.

Under its rules, Royal Mail is required to deliver 93% of first class mail within one working day of collection and 98.5% of second class mail within three working days of collection.

However, in 2021/22, Royal Mail fell short of both targets and delivered 81.8% of first class mail within one working day and 95.4% of second class mail within the timeframe.

In February, data from charity Citizen’s Advice found a staggering 2.5 million people missed important documents, health appointments, or were unable to pay a fine or bills over Christmas due to Royal Mail’s delivery failures. In total, it said 15 million people were left waiting for post over the festive period.