The union, which represents 100 members of staff based at Liverpool, claims Royal Mail is "abandoning" Liverpool.
In a statement, Royal Mail denied that redundancies would occur. It said: "We will be working with staff and their representatives to offer a range of options for those who change what they do. This could include working at another unit in the same town or moving to a unit elsewhere.
"We hope that, given existing staff turnover, with flexibility everyone who wants to continue to work for Royal Mail will be able to do so."
Brian Scott, assistant national secretary for Unite, said: "We will be seeking an early meeting with Royal Mail to examine, in fine detail, the costing assumptions that have been used."
Union predicts Royal Mail redundancies
Royal Mail is to move its sorting offices in Crewe and Liverpool to Warrington, resulting in compulsory redundancies, according to Unite.
