Progressive Senator Bernie Sanders launched an investigation into charges of unsafe working conditions at Amazon.com Inc. warehouses across the US, raising the possibility of high-profile hearings on complaints over the retailer’s treatment of employees.

Safety issues at Amazon’s warehouses have been a flashpoint between the company and labor activists. The Labor Department’s Occupational Safety and Health Administration in February cited the company for violations of safety laws at warehouses in three states.

Sanders, who chairs the Senate committee with jurisdiction over labor laws, portrayed the company as maintaining its position as one of the world’s most valuable companies at the expense of its workers’ well-being, saying Amazon employees suffer higher injury rates than comparable workers elsewhere.

Sanders, a Vermont independent who is leading champion of progressive causes, asserted the company endangers its workers by requiring them to navigate narrow warehouse aisles, lift heavy boxes and engage in repetitive movements without adequate breaks.

“The company’s quest for profits at all costs has led to unsafe physical environments, intense pressure to work at unsustainable rates, and inadequate medical attention for tens of thousands of Amazon workers every year,” Sanders said in a letter Tuesday to Amazon.com CEO Andy Jassy.

Amazon spokesperson Steve Kelly defended the company’s safety record, saying the retailer has invested more than $1 billion in safety initiatives over the past four years and reduced injuries 23% in US operations since 2019. Amazon is the nation’s second-largest private employer, after Walmart Inc.

Sanders in his letter cited data that found Amazon workers sustained nearly 39,000 workplace injuries in 2022, 95% of which caused them to lose work hours or modify their duties. The rate of injuries is 6.6 injuries per 100 workers, more than double the rate at non-Amazon warehouses, according to a report from the Strategic Organizing Center, a coalition of major labor unions.

“If Amazon can afford to spend $6 billion on stock buybacks last year, it can afford to make sure that its warehouses are safe places to work,” he wrote.

It’s the second time this year that Sanders has taken on a major company over its labor-related practices. In March, Starbucks Corp.’s recently departed chief executive officer, Howard Schultz, testified under threat of subpoena before Sanders’ committee. Schultz forcefully defended the company’s response to union organizing, rejecting a labor-board judge’s ruling that the company had committed “egregious” violations of the law.

Sanders announced his panel has set up a web page for Amazon employees to make confidential reports of the company’s safety performance, a sign the committee is seeking cases to highlight in public testimony or reports.

--With assistance from Leah Nylen.