Amazon pushes its US warehouse workers to fulfill orders at speeds that could cause high rates of injury despite being aware of the risks, an investigation led by Senator Bernie Sanders has found.
The findings, external, following an 18-month probe of the firm, support claims that workers and labour campaigners have made about the company for years.
The report accused the firm of rejecting changes that would have reduced workers' pace, but improved safety because of concerns about its bottom line.
But Amazon said, external the report was "wrong on the facts", and featured "selective, outdated information that lacks context and isn't grounded in reality".
"This investigation wasn't a fact-finding mission, but rather an attempt to collect information and twist it to support a false narrative," the company said.
Amazon, which employs roughly 800,000 people in the US, has faced accusations about unsafe conditions at its warehouses for years.
Those concerns ramped up during the Covid pandemic, when e-commerce exploded, leading to protests by its workers around the world.
Amid the controversy, founder Jeff Bezos said the company needed to do better by its employees.
Senator Sanders, who is known for his pro-worker stance, launched an investigation into Amazon's practices in June 2023. Senate staffers conducted 135 interviews and reviewed more than 1,000 documents.
Their analysis of public records found that warehouses operated by Amazon recorded over 30% more injuries than the warehousing industry average in 2023.
Amazon workers were also nearly twice as likely to be injured than people working in warehouses operated by other companies in each of the last seven years, according to the report, which was signed off by Democratic members of the Senate's Committee on Health, Education, Labor and Pensions.
Amazon had internally examined connections between workplace speed and injury rates, including in a review called Project Soteria, according to the investigation.
But the report said the company opted not to adopt the recommended changes, which included providing more time off to workers, and halting disciplinary action against people who did not meet working speed requirements.
Investigators also accused Amazon of trying to "manipulate" data to mislead the public about its safety record.
Amazon said it was fair for the firm to focus safety comparisons on larger warehouses.
It accused the Senate investigation of ignoring inconvenient facts, such as a decline in its injury rates and a recent court victory, which dismissed safety complaints.
It said another team asked to review the recommendations of Amazon's internal safety study had found that the methodology was "unsound".
"Nothing" is more important to the firm than employee safety, Amazon said.
"Sen. Sanders and his staff chose to rely on the debunked Soteria analysis because it fits the false narrative he wanted to build," the company added.