Late-summer strikes by 115,000 Royal Mail workers have moved a step closer after an overwhelming vote in favour of walkouts, threatening massive disruption to postal deliveries across the country.
The Communication Workers Union (CWU) said 97.6% of members who voted backed strikes in a 77% turnout, threatening the biggest strike action in the so-called summer of discontent to date based around the cost of living crisis.
The union suggested it was the greatest strike mandate it had ever won from Royal Mail workers.
However, no strike dates were announced in response to the ballot - allowing more time for a negotiated settlement.
The CWU demanded Royal Mail enter talks to agree a "straight, no-strings" pay rise.
The company responded by accusing the union of a failure to engage on the changes it needs to adapt to the modern postal market.
"The vote can leave no doubt that postal workers are united, and that they are demanding the proper pay rise they deserve," the union said.
The result was announced 24 hours after a separate dispute at the company eased back from the brink of strike action.
A three-day walkout by 2,400 managers, due to start on Wednesday, was called off by Unite after a ballot on new proposals to help end their row with bosses over jobs, pay and conditions.
The CWU remains locked in several pay disputes, including one at BT and at the Post Office.
It is part of a union campaign for pay awards in line with soaring inflation, which stands at a 40-year high of 9.1%.
The Royal Mail dispute is not only about pay but conditions attached to the company's offer.
Royal Mail boss Simon Thompson told Sky News last month that it had offered a 5.5% pay rise and already passed on, with no strings attached, a 2% increase to help its workers navigate the cost of living crisis while talks with the CWU continued.
This suggested that the remaining 3.5% on the table was conditional on the union accepting the company's need to modernise as it aims to become a parcels-focused business due to the gradual decline in letter volumes.
The company is also understood to have offered a new "above and beyond" bonus.
A Royal Mail spokesperson said in response to the vote: "We are disappointed that CWU members have voted in favour of industrial action.
"We offered a deal worth up to 5.5% for CWU grade colleagues, the biggest increase we have offered for many years, which the CWU rejected.
"We can only fund this offer by making the changes that will pay for it and ensure Royal Mail can grow and remain competitive in a fast-moving industry.
"Despite nearly three months of talks, the CWU have not engaged in any meaningful discussion on the changes we need to make to adapt.
"Ensuring we can change, at pace, is the route to protecting well-paid, permanent, jobs long term and retain our place as the industry leader on pay and terms and conditions.
"That is in the interest of Royal Mail and all its employees.
"In the event of industrial action, we have contingency plans to minimise customer disruption and will work to keep people, businesses and the country connected."