Thousands of Royal Mail managers are to be balloted over possible strike action in a dispute over job cuts.
About 8,500 managers at Royal Mail head offices across the UK, and those at subsidiary businesses Parcelforce and the Post Office are due to vote.
The Unite union said it was the first time in more than 30 years that postal service managers had been asked to decide on whether to hold walkouts.
Royal Mail said some job cuts were essential due to falling mail volumes.
Unite said the ballot had been organised in protest at what it said were plans to cut 1,500 manager positions on a compulsory basis.
Paul Reuter, national officer at the union, said: "Unite will not allow managers to be forced out because of the poor decisions made at the very top of Royal Mail Group.
"If Royal Mail are allowed to push ahead with forced redundancies it will keep coming back for more, so Unite intends to stop Royal Mail in its tracks."
He added that the Royal Mail had already cut 5,000 jobs over the past five years on a voluntary basis, and that, as a result, compulsory redundancies were "not necessary now".
A Royal Mail spokesman said: "We continue talking with Unite, and have stressed we will continue doing our utmost to manage any job losses by voluntary means."
The government announced last month that it is to move ahead with plans to privatise the Royal Mail, saying it needed both private finance and expertise.