Ever since Amazon overtook Wal-Mart as the world’s largest retailer in 2015, things have been on the up and up for the e-commerce giant.

Its founder, Jeff Bezos has gone from a technology industry success story into the richest man in the world, based largely on the value of his Amazon ownership. The company, which Bezos founded in his garage in 1994, has grown tremendously over the past two decades.

However, a new undercover report from the Sunday Mirror reports that the rapid growth of the e-commerce giant may have come at a cost, with difficult conditions for workers in many of the company’s fulfilment centres.

Photographs and video taken by an undercover reporter show Amazon workers falling asleep while standing up at their stations. Workers at many of Amazon’s fulfilment centres are held to strict standards, with some reportedly required to process a parcel every 30 seconds.

Alan Selby, who spent five weeks at the company’s fulfilment centre in Essex, noted that some workers had been rushed out of the warehouse by ambulance after collapsing at work after long shifts and demanding weekly house.

The investigative reported claims that AMazon treats its workers as “expendable commodities”, and that humans are viewed as the least efficient part of the company’s operations.

Employees at the warehouse are reportedly required to work as many as 55 hours a week, with timed toilet breaks and challenging targets for fulfilling orders. Workers, who are paid £8.20 per hour, are required to pack as many as 120 items per hour.

This target is reportedly set to rise to 200 items per hour, further increasing the strain placed on workers at the e-commerce company’s fulfilment centres.

Workers at the Essex centre are reportedly discouraged from sitting during their shifts, which can extend for as long as 10 hours per day. Productivity metrics, such as a worker’s “units per hour” are continually displayed to encourage maximum efficiency.

The undercover report isn’t the first to document difficult conditions for Amazon workers. An earlier report carried out by a BBC reporter, who worked undercover at an Amazon depot for several weeks, found that the company’s drivers were under severe pressure to meet targets.

Drivers reportedly exceeded the speed limit to make deliveries on time, as well as urinating in bottles due to limited time for toilet breaks. Despite these issues, some drivers claimed to find the job “sometimes enjoyable” due to customer satisfaction.

In a statement, Amazon notes that it “provides a safe and positive workplace with competitive pay and benefits from day one.” The e-commerce company is “proud to have created thousands of permanent roles in [its] UK fulfilment centres in recent years.”

“We offer great jobs and a positive environment with opportunities for growth. As with most companies, we expect a certain level of performance.”

“Targets are based on previous performance achieved by our workers. Associates are evaluated over a long period of time as we know a variety of things could impact the ability to meet expectations in any given day or hour.”