"The Communication Workers Union (CWU) has made it clear to Royal Mail Group that unless we seriously revisit failed revisions, restore quality of service and end USO (universal service obligation) failures the business will not succeed," the union said in a statement.

"Royal Mail Group committed to this as the first step of the agreement but their ongoing actions and what you are seeing and feeling in the workplace do not in any way reflect this."

Royal Mail did not immediately respond to a Reuters request for comment.

(Reporting by Eva Mathews in Bengaluru; Editing by Vinay Dwivedi)