Ben Fox Rubin/CNET

A group of 13 members of Congress on Tuesday asked the Department of Labor to investigate all of Amazon's US warehouses, citing a long list of concerns about working conditions, labor violations, injuries and mistreatment.

The group is led by Vermont Sen. Bernie Sanders, a Democratic candidate for president, and Rep. Ilhan Omar of Minnesota. The members are all Democrats except Sanders, who's an independent, and include prominent party members including Congresswoman Alexandria Ocasio-Cortez and presidential candidate Tulsi Gabbard.

In a statement Tuesday, Sanders called on the Labor Department's Occupational Safety and Health Administration to open an investigation immediately and "prosecute those responsible to the fullest extent of the law."

"People who work for a company owned by the wealthiest person in America should not have to risk their lives, health or well-being on the job," he said, referring to Amazon CEO Jeff Bezos. "They must be treated with dignity and respect."

Amazon shot back Tuesday, saying Sanders has an open invitation to visit its warehouses "but to date has never stepped foot in one of our buildings." The company said if Sanders had seen the facilities, he'd have learned that the company already implemented multiple layers of safety protocols at its warehouses. That work includes monthly employee surveys of safety, more than 1 million hours of safety training last year, and $55 million in safety improvement investments in the past year.

"The allegations outlined in this letter are not an accurate portrayal of activities in our buildings," Amazon said, adding that people as young as 6 can tour the buildings to see for themselves.

Sanders rejected Amazon's suggestion, saying in a tweet Tuesday afternoon he preferred surprise inspections be conducted by the Labor Department.

"I am not interested in a photo op at an Amazon warehouse," Sanders' tweet said. "I am calling for Labor Department inspectors to come in, unannounced, and do thorough investigations of the facilities where hundreds of workers have told me about horrendous conditions and abuse."

The congressional request continues long-running criticisms of how Amazon operates its warehouses, with years of news reports detailing employees being overworked, closely monitored and forced to move faster. While Amazon has faced heavy criticism in the press and from several members of Congress, a comprehensive government report on its warehouse conditions hasn't happened.

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Sanders' criticisms follow his repeated attacks against Amazon last year, when he called on the company to raise its minimum wage. When it did in October, he congratulated it for making that change.

The congressional group sent a letter requesting an investigation during Prime Day, Amazon's annual summer sale. In its fifth year, Prime Day has started to garner plenty of negative attention, with protests going on across the US and Europe on Monday.

On Wednesday, a Department of Labor spokesperson said: "OSHA has confirmed receipt of the letter. The agency is still reviewing the letter at this time."

I stand in solidarity with the courageous Amazon workers engaging in a work stoppage against unconscionable working conditions in their warehouses. It is not too much to ask that a company owned by the wealthiest person in the world treat its workers with dignity and respect. https://t.co/GxagHx70pb — Bernie Sanders (@SenSanders) July 15, 2019

Amazon said Monday that Prime Day has "become an opportunity for our critics, including unions, to raise awareness for their cause, in this case, increased membership dues." The company has often mentioned that it raised its minimum wage to $15 last year and offers a comprehensive benefits package that includes paid education, parental leave and opportunities for promotion.

Amazon's roughly 300,000 US employees aren't represented by unions.

In Tuesday's letter to OSHA, the members of Congress outlined several workplace problems they want investigated, including a report from Mother Jones that highlighted hazardous warehouse floor conditions that can cause long-term injuries. The group said they've heard hundreds of stories directly from people who worked for Amazon that present extremely poor conditions for employees, including high temperatures, closely monitored productivity that causes workers to avoid bathroom breaks for fear of falling behind, mental health issues, and calls for a faster pace that ultimately lead to injuries.

One former worker, a Navy veteran, said, according to the letter: "There was a point where I would find myself crying on my shift ... I really felt like I just didn't wanna be alive anymore."

"This work environment creates a high risk of physical injuries, a risk increased by Amazon's intentional disregard for the health and safety of their employees," the letter said.

In addition to Omar, Sanders, Gabbard and Ocasio-Cortez, Reps. Rashida Tlaib, Deb Haaland, Ayanna Pressley, Barbara Lee, Jan Schakowsky, Ro Khanna, Al Green, Debbie Dingell and Andy Levin joined the call for an investigation and signed the letter to OSHA.

Originally published July 16, 9:41 a.m. PT.

Update, 11:59 a.m. and 4 p.m. PT on July 16: Adds Amazon's comments and Sanders' response to Amazon invitation. Update, 1:10 p.m. PT on July 17: Adds OSHA comment.