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U.S. senators are scrutinizing Amazon’s handling of its warehouse workers amid the COVID-19 outbreak.

Four legislators sent a letter to Amazon CEO Jeff Bezos Friday outlining their concern for the safety of employees who help pack and ship customer orders.

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Sen. Cory Booker (D-N.J.); Sen. Bernie Sanders (D-VT); Sen. Bob Menendez (D-N.J.); and Sen. Sherrod Brown (D-OH) cited recent stories about Amazon warehouse workers saying they feel unsafe. BuzzFeed spoke with employees who said there aren’t enough sanitation supplies, and that “stand-up” staff meetings with workers in small areas are ongoing.

“Any failure of Amazon to keep its workers safe does not just put their employees at risk, it puts the entire country at risk,” the letter notes, citing that the novel coronavirus can live for up to 24 hours on cardboard and up to three days on plastic and stainless steel.

“That means that Americans who are taking every precaution, staying home and practicing social distancing, might risk getting infected with COVID-19 because of Amazon’s decision to prioritize efficiency and profits over the safety and well-being of its workforce.”

The senators ask for a written response to six questions by no later than March 26, including whether Amazon will agree to cover the cost of COVID-19 testing for employees and if the company will shut down facilities where a worker tests positive.

Amazon called the accusations “simply unfounded.” Here’s the full statement the company shared with GeekWire:

“These accusations are simply unfounded. Our employees are heroes fighting for their communities and helping people get critical items they need in this crisis. Like all businesses grappling with the ongoing coronavirus pandemic, it is not easy as supplies are limited, but we are working hard to keep employees safe while serving communities and the most vulnerable. We have taken extreme measures to keep people safe, tripling down on deep cleaning, procuring safety supplies that are available, and changing processes to ensure those in our buildings are keeping safe distances.”

The first known case of an infected worker at a U.S. Amazon warehouse was reported by The Atlantic on Wednesday. Amazon closed the Queens, N.Y. delivery station and associates were sent home with full pay.

At least five workers at Amazon warehouses in Europe have tested positive for COVID-19, according to Bloomberg.

Under the strain of high demand as more people turn to online shopping during the coronavirus crisis, Amazon is implementing preventative health measures for employees, delivery and transportation partners at sites around the world. They include increasing frequency and intensity of cleaning at all sites; adjusting practices to ensure social distancing; requiring employees to stay home and seek medical attention if they are feeling unwell; and more.

The company has previously said that any employees who are diagnosed with COVID-19 or placed into quarantine will receive up to two weeks of pay. It is also offering unlimited unpaid time off for hourly workers until March 31.

Amazon earlier this month said it will donate $25 million to help its network of independent delivery drivers, Amazon Flex workers, and seasonal employees deal with disruptions caused by the COVID-19 outbreak.

As the top online retailer in the U.S., Amazon has become a key player in the COVID-19 outbreak that is driving a spike in online shopping as thousands of people avoid leaving their homes. The company is responsible for 38.7 percent of online sales in the U.S., according to eMarketer. Walmart is second with 5.3 percent.

Amazon announced this week that it plans to add a whopping 100,000 warehouse workers to keep up with orders.

Update: Amazon said it will increase overtime pay for warehouse workers between March 15 and May 9, according to Reuters.