Bernie Sanders has launched an investigation into Amazon that will focus on working conditions inside the warehouses of the online marketplace, which is also the nation’s second-largest employer.

In a letter to Amazon CEO Andy Jassy, the 81-year-old US senator from Vermont and chair of the influential Senate committee on health, education, labor and pension (Help) demanded information about “systematically underreported” injury rates, turnover, productivity targets, and adherence to federal and state safety guidelines at the e-commerce giant.

Sanders’s letter, which was obtained by the Washington Post, described conditions at Amazon’s warehouses as “uniquely dangerous” and pointed to a report that found the company’s serious injury rate in 2021 was double the warehouse industry average in 2021.

“Amazon is one of the most valuable companies in the world, worth $1.3tn and its founder, Jeff Bezos, is one of the richest men in the world worth nearly $150bn,” Sanders wrote in the letter. “Amazon should be one of the safest places in America to work, not one of the most dangerous.”

Amazon spokesperson Steve Kelly acknowledged that the company had “received chairman Sanders’s letter this evening and are in the early stages of reviewing it”, adding that the senator had an open invitation to tour one of the company’s warehouses.

Sanders has previously hit out at working conditions and pay at Amazon. In 2018, the company said it would raise its base hourly pay rate to $15, or roughly double the national minimum wage. Then CEO Jeff Bezos said the company had “listened to our critics”.

The initiation of an investigation into workplace health and safety practices at Amazon comes amid a vigorous opposition against unionization efforts by company employees and data from the Occupational Safety and Health Administration that Amazon warehouse jobs can be more dangerous than at comparable companies.

Over the past year, Amazon has opposed union organizing campaigns, resisted charges of unfair labor practices filed by workers and spent over $14.2m on anti-union consultants in 2022.

“It’s one of the companies that really talks about a big game about how good they treat their workers, and yet, when you actually talk to workers, it’s the total opposite,” Aliss Lugo, an organizer in Georgia with United for Respect at Amazon, told the Guardian in April.

Sanders has previously written a letter to Starbucks founder and former CEO Howard Schultz in which he accused the coffee company of refusing to bargain a contract with workers who voted to unionize.

“Over the past 18 months, Starbucks has waged the most aggressive and illegal union-busting campaign in the modern history of our country,” Sanders stormed at a Help committee hearing in March.

In an interview with the Post, Sanders said it was “an absolute possibility” that Jassy or founder Jeff Bezos could be called to testify at a similar hearing, as Schultz had done.

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“Amazon sets an example for the rest of the country,” Sanders said. “What Amazon does, their attitude, their lack of respect for workers permeates the American corporate world.”

Sanders told the Post he was “appreciative” of Amazon’s decision to raise its starting wage but maintained he was “extremely upset by their vehement anti-union behavior” and workplace safety record.

Steve Kelly, the Amazon spokesperson, said the company has recorded a 23% reduction in injuries since 2019 and had invested more than $1bn into safety initiatives, projects and programs in the last four years.

“We’ll continue investing and inventing in this area because nothing is more important than our employees’ safety,” Kelly added, and he said that critics of the company had spliced the data “to suit their narrative”.