Amazon has reported more than 440 health and safety incidents at its UK warehouses since 2015, according to Freedom of Information (FoI) requests.
The GMB union requested information from local authorities throughout the UK.
It discovered that workers had suffered fractures, head injuries, contusions, and collisions with heavy equipment.
Amazon said it was a safe place to work and that reports to the contrary were "simply wrong".
Rise in accidents
According to the data collected from the FoI requests, in 2015-2016 there were 80 health and safety incidents.
This number rose to 114 in 2016-2017, and then to 149 in 2017-2018.
So far in 2018-2019, there have been 99 health and safety incidents.
The GMB said the actual numbers were probably higher, because some local authorities were unable to provide details of incident reports.
Amazon said that in 2015, it had eight fulfilment centres in the UK, but now it has 17.
Examples of some of the accidents reported include:
- A forklift driver crashed into a steel column at a warehouse in London, almost causing a floor above to collapse
- A worker in Leicestershire sustained injuries after being knocked down and wedged under a reversing heavy goods vehicle
- Staff worked in temperatures as low as 3C at a Dundee warehouse
- A worker was injured using their hand to remove a jammed label from a conveyor belt in Peterborough
Amazon have disputed the examples the GMB have highlighted.
The company said that all employees work within regulated hours, that the company's heating systems meet the official requirements and that the health and safety authorities had decided not to take action in a number of incidents put forward by the GMB.
The FoI requests also revealed that Amazon employees had made complaints to local authorities about working conditions.
In one case, delivery drivers at the warehouse in Peterborough complained that they were made to wait in an unheated room for eight to ten hours, with access to only one unisex toilet and no other facilities.
Debate over incidents
An Amazon spokesman said the company had 43% fewer injuries on average than other transportation and warehousing companies in the UK.
Health and Safety Executive (HSE) figures show that in 2016-2017, in the warehousing and transportation support industries, there were 1,577 reported non-fatal injuries per 100,000 workers.
"Amazon is a safe place to work and reports to the contrary are simply wrong," he said.
"Amazon has created more than 25,000 good jobs with good pay and benefits across Britain and we are proud of the work they do on behalf of customers every day."
"Amazon's claims over its health and safety record have not been independently verified, and there are good reasons to doubt that they are accurate," a GMB spokesman told the BBC.
"GMB's investigations at the Rugeley warehouse in Staffordshire suggests that the serious injury rate may be significantly higher than the sector average.
"If it wants to be taken seriously, Amazon should publish its own health and safety data and recognise GMB so workers have an independent voice through which to raise their serious concerns."