It demanded that the company negotiate to secure an “instant, no-obligation pay increase” for employees.
A spokesman for the CWU said: “British postal workers are being forced to accept a massive pay cut from the same people for whom they have made incredible profits.
“Our members go to food banks while bosses reward themselves with advance bonuses. It is an unjust, untenable way of treating people.
“We have no doubt that workers will defy this despicable treatment, stand up for themselves and vote to start the biggest strike of this summer.”
The CWU is also involved in wage disputes at BT and the post office, with union bosses threatening a “summer of discontent” over the cost of living crisis.
Rail and tube networks were plunged into chaos last week when the Rail, Maritime and Transport union staged the largest strike in more than thirty years.
Britons face further disruptions, with more railway strikes planned alongside strikes by airport and bus workers.
Inflation is expected to rise above 11 pc later this year. rise when the energy price ceiling rises again.
Royal Mail has been contacted for comment.