Conditions for workers at Amazon warehouses could cause mental and physical illness" according to an investigation by BBC Panorama.
The show secretly filmed the working conditions endured by undercover reporter Adam Littler at the retailer's Swansea depot.
Each shift can involve up to 11 miles of walking with orders expected to be picked every 33 seconds with a handset beeping a warning signal if this schedule is not adhered to. Performance is monitored by these machines and automatically fed back to managers.
"The characteristics of this type of job, the evidence shows increased risk of mental illness and physical illness," Prof Michael Marmot told the show.
"There are always going to be menial jobs, but we can make them better or worse. And it seems to me the demands of efficiency at the cost of individual's health and wellbeing – it's got to be balanced."
Amazon has denied the accusations, pointing out that it adheres to all employment laws.
We strongly refute the charge that Amazon exploits its employees in any way,” it said. The safety of our associates is our number one priority, and we adhere to all regulations and employment law.
We provide competitive wages and stock grants which over the past five years have added an average of 12 per cent to base pay annually. This means that, on average, an Amazon associate with two years' service will be earning 8.98 per hour for a day shift or 10.78 per hour for a night shift. Additionally, we provide a raft of benefits.
Amazon has retained an independent expert who has visited our buildings and associates. In the independent expert's opinion, a picking role is similar to jobs in many other industries and does not increase the risk of mental and physical illness.
Amazon is proud to have a highly favourable safety rate compared to companies in the same industry. From April 2012 to October 2013, Amazon's RIDDOR rate (the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations” as defined by the UK Health and Safety Executive) was less than 40 per cent of the average for companies reporting under the same industry code.
We understand that our progress depends on good execution and good judgment from thousands of employees. Together, we're working hard to make sure that we are better tomorrow than we are today.”
Amazon has employed an additional 15,000 workers for the Christmas period.