A former worker at Amazon's Swansea warehouse has claimed staff are treated "like robots" and routinely sacked for not meeting "unrealistic targets".
It comes as a union demanded talks with the online giant over safety and working conditions there.
Since 2015-16, there have been 84 serious incidents reported to the Health and Safety Executive (HSE) - the second highest of Amazon's UK centres.
Amazon says it has 43% fewer injuries on average than other firms' depots.
Amazon in Swansea employs 1,200 permanent staff and hires more than 2,000 temporary staff at Christmas.
The worker, who did not want to be identified, said it was an "intimidating" place to work.
He told Welsh language news programme Newyddion 9: "Things like timed breaks, constantly monitoring you. Not being able to have the freedom to go to the toilet without someone coming and being like, 'right, you've been five minutes away from your task now what have you being doing?'.
"You are essentially a robot trying to get everything 100% perfect, and if you don't meet those standards then you know about it.
"I'd say they treat you like a number and they treat you like robots, and after a while, because of the brain numbing work, you become a little bit of a robot as well.
"When it got closer to Christmas there were people getting let go every week. I saw people getting sacked around me, they'd get asked to meet their line manager and I wouldn't see them again.
"You were very aware that you were part of an expendable workforce."
The GMB Union, which made the claim about the number of health and safety incidents at the site, said the figures spoke for themselves.
Regional organiser Jeff Beck said: "People are under so much pressure there they've been dehumanised, they've been turned into robots, and that's when the accidents are occurring."
Nic Fyfe, Amazon's regional operations director, said: "I welcome scrutiny, I think that's an important part of what we do, but I do not recognise the stories that I see in the press."
Malcolm Rees, who has worked at the Swansea centre for seven years, said people have only heard bad stories about Amazon, but there was "enjoyment" and career opportunities.
"We take pride in our buildings as safe places to work," said an Amazon spokeswoman.
She added: "Associates are allowed to use the toilet whenever needed."
The spokeswoman also said they evaluate performance over time and coach anyone underperforming to help them improve.