“You work a lot and end up tired and get asked, “Why did you not reach the target?'. You feel useless.”

“You were told off if you spoke to people during your shift…you were not allowed to wear hoodies in case you used them to steal something.”

These are just a few of the comments made by Amazon employees in Scotland about the conditions they work under. The company, much criticised for paying too little tax in recent years, is once again back in the spotlight following revelations about working practices in the US.

A shocking investigation found an “abusive corporate culture” among white collar staff at Amazon’s campus in Seattle, with employees breaking down and crying at their desk, and some with serious illnesses being told their job performance is under review.

And in Scotland, unions and employment campaigners have now also raised concerns about workers in the company’s warehouses being driven to “breaking point” trying to meet the demands of the job.

Martin Smith, national organiser of the GMB union, said the general culture of “overbearing management” identified in the US report was a common theme in the company’s warehouses in the UK.

“It creates a workload and a work place that we are very concerned about," he said. "Some of our members report, for example, they effectively run a half-marathon every shift."

The union is not recognised in Amazon, which Smith claims is due to a culture of “fear” that members will lose their job. For many, he says, an Amazon job is better than nothing - even though conditions are comparable to that of a "19th century cotton mill".

“They are jobs of last resort, but in the kinds of communities Amazon descends upon they are desperate for employment, such as the couple of big sites in Scotland,” he said.

“We are not calling for a boycott, but we are making sure that people understand what it is they are supporting.

“Amazon Prime can get you a new coat and deliver it in 24 hours on a Sunday, but behind that is lots of people being very badly exploited and run into the ground to pack those boxes. Customers have to at least be aware of that.”

Amazon has grown from a website which began selling books in 1995 to become the largest retailer on the web, which recently overtook Walmart in terms of value.

Behind its slick hi-tech customer website, much of the business relies on vast warehouses. Two of these ‘fulfilment centres’ are situated in Scotland – the first was opened in Gourock in 2004 and is the size of four football pitches. In 2011, another was opened in Dunfermline – this time the size of around 14 football pitches.

These warehouses are packed with shelves stacked with millions of products. Job roles include those who pack the items and pickers, who carry around handheld gadgets which show where a product is located – which can also monitor the employee’s productivity.

One employee, who did not want to be identified, told the Sunday Herald: “On one hand I feel grateful to have the opportunity to work for such a successful company.

“But there is also a feeling of frustration which I hear every day – the expectations they have of you are too high – you are expected to work very, very fast, and people hardly reach the targets.”

There is no doubt thousands of permanent and temporary jobs have been created by Amazon’s presence - the company was given more than £10 million of funding by Scottish Enterprise towards setting up its operations in Scotland.

But campaigner Jim McCourt, of the Inverclyde Advice and Employment Rights Centre, is also concerned about the company’s working practices.

He said he has dealt with cases concerning employees at the Gourock site – but details cannot be revealed as many are too scared they will lose their jobs.

“In general, I think the workers are driven to breaking point in there,” he said. “Workers are in a particularly unique situation in that the people who do the picking are timed as well. You can get pulled up if you spend too long in any given aisle, for example.

“The speeds they are required to go at average between 10 and 12 miles a night – at any given point you can be given points towards a disciplinary if you are not quick enough.”

McCourt also said many workers were caught in a “poverty trap” and risked having benefits sanctioned, for example, if they declined to take a job with the company.

Labour Dunfermline MSP Cara Hilton said that if Amazon "had nothing to hide" then it should start working with trade unions and "give workers a real voice".

She added: “People aren’t machines and their health, safety and wellbeing is important – Amazon needs to be making sure that is a priority.”

Ian Brinkley, chief economist at The Work Foundation, an independent employment research charity, said public opinion could put pressure on companies like Amazon.

“They don’t like being held up as bad employers, particularly as Amazon has been trying to protect this image of being the hi-tech new kid on the street and the idea they are exploiting workers is not good for that,” he said.

“The countervailing pressure is we still buy lots of stuff on Amazon, even if we don’t particularly like the way they are treating their workforce – low prices tend to be quite a driver.

“It is the competition between those two forces which is ultimately going to drive any real changes in employment practices within the company.”

Amazon, meanwhile, has been vigorously defending its track record. Founder Jeff Bezos wrote to staff in the wake of the American investigation saying: “I don’t recognise this Amazon and I hope you don’t either.”

The Sunday Herald requested a visit to one of Amazon’s centres in Scotland, but was told it could not be arranged at short notice.

In response to the criticisms, the company said it enjoyed a good relationship with its workforce through its employee forums. It also pointed to a statement on its website which outlines a starting pay scale of £7.39 for permanent employees and £6.70 for the first 12 weeks for temporary employees.

It said it does not use zero-hour contracts but has an agreement with agencies that full-time employees will be paid for no less than 20 hours of work per week.

The statement said that from April 2013 to March 2014, Amazon had a 40% lower rate of reported safety incidents than other companies in the same industry.

On the issue of targets it stated: “Productivity targets are set objectively, based on previous performance levels achieved by our workforce.”