Unions have intensified pressure on Royal Mail to relent in its ongoing pay dispute with postal workers by publishing documents showing managers at "breaking point".
While major private sector union Amicus has said post office managers are being forced to work under conditions of extreme stress for too little pay, the Royal Mail has insisted its employees are not treated unfairly.
Amicus called for a meeting with Royal Mail chairman, Allan Leighton, to discuss working conditions in the firm.
"Royal Mail must stop making any further redundancies and start paying attention to looking after the health of their hard pressed managers," commented Amicus' assistant general secretary, Paul Talbot.
"The long hours culture within the Royal Mail is taking its toll and postal managers are reaching breaking point. Royal Mail are putting the health of their staff at risk and jeopardising the excellent service the Royal Mail gives to the public and British business."
Pressure from Amicus comes on the back of a vote last week by members of the Communication Workers Union (CWU) calling for industrial action over an imposed wage rise of 2.9 per cent.
Around 136,000 postal workers voted last week, setting up what would be Britain's first national postal strike in over a decade.
The union said that the dispute also concerned Royal Mail's failure to alter working practices and plans to make thousands of its employees redundant.
The current industrial conflict comes on the back of longer-term concern over the development and potential introduction of new sorting machinery which could see the deprivatised group cut its costs significantly.
Royal Mail postal workers would pay the price for that economising, which could reduce the human resource requirements in the company by 50 per cent – totalling 40,000 jobs.