Amazon Prime Day, the 48-hour discount blitz that kicks off Tuesday, is a “major” cause of worker injuries, according to the preliminary results of a Senate probe.

The Senate’s Health, Education, Labor and Pensions (HELP) Committee on Tuesday released the interim results of a yearlong investigation into Amazon’s warehouse working conditions just as the company holds its annual Prime Day deals event.

Amazon provided the committee with internal data from Prime Day 2019 that showed its total injury rate, including those the company is not required to disclose to the Occupational Safety and Health Administration, was “just under” 45 injuries per 100 workers, which amounts to “nearly half of the company’s warehouse workers,” the report states.

“Amazon continues to treat its workers as disposable and with complete contempt for their safety and wellbeing,” Sen. Bernie Sanders, a Vermont independent who chairs the HELP committee, said in a statement. “That is unacceptable and that has got to change.”

According to the report, the internal data provided by Amazon shows that its warehouses have been understaffed during Prime Day and the holiday shopping seasons, “endangering workers who have to manage increased volume without increased support,” according to the report. The report cites an internal Amazon document, titled “2021 Prime Day Lessons Learned,” which states Amazon “met only 71.2 percent of its hiring target,” between May and June of 2021, ending the week of that year’s Prime Day event.

Amazon spokesperson Kelly Nantel said the report ignores the progress Amazon has made.

“It draws sweeping and inaccurate conclusions based on unverified anecdotes, and it misrepresents documents that are several years old and contained factual errors and faulty analysis,” Nantel said. “For example, one of the false claims in the report implies that we’re not adequately staffed for busy shopping periods.” Nantel added that, since 2019, Amazon has reduced its incident rate for anything requiring more than basic first aid by 28% in the U.S. and lost time incident rate, which includes more significant injuries requiring an employee to miss at least one day of work, by 75%.

Amazon has faced scrutiny in recent years over its workplace injury record and its treatment of warehouse and delivery workers. It’s been cited by federal regulators for safety violations. OSHA and the U.S. Attorney’s Office are investigating conditions at several warehouses, while the U.S. Department of Justice is examining whether Amazon underreports injuries. 

The company said in March that its injury rates have improved, and it announced plans to invest more than $750 million in safety initiatives this year. It has also appealed a string of citations issued by OSHA around safety hazards and violations.

Amazon has said it’s begun to automate some tasks and is also rolling out more robotic systems in warehouse facilities that the company says can improve safety, although that prospect has been debated.