Postal workers have overwhelmingly voted in favour of strike action in a dispute over pay.
The Communication Workers Union (CWU) said 97.6% of members who voted in the ballot backed strikes, with a 77% turnout.
No date has been set for the industrial action, which could lead to 115,000 Royal Mail workers walking out later this summer.
A separate three-day strike by 2,400 Unite members due to start on Wednesday was called off after new proposals were put forward on jobs, pay and conditions.
It comes as warnings mount over a "summer of discontent" as unions prepare for clashes with Government over pay and working conditions.
CWU General Secretary Dave Ward said there will now be a "small window" of opportunity for talks to avoid walkouts before strike dates are set.
He said postal workers received big support from the public for their efforts during the pandemic and would continue to receive backing for their pay campaign.
"While bosses rake in £758m in profit and shareholders take £400m, workers are expected to take a serious real-terms pay cut," he said.
"Postal workers won't accept their living standards being hammered by bosses who are typical of business leaders today - overpaid, under qualified, out of their depth.
"In our country right now, corporate failure gets rewarded over and over again.
"It's pathetic that CEOs take home lottery win salaries then offer real-terms pay cuts to people who made them their profit."
It comes as inflation hit 9.1% in May, the highest level in 40 years, raising pressures on household budgets.
A Royal Mail spokesperson said: "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.”
