Elizabeth Warren, other Massachusetts Democrats probe Walmart on store with more than 80 coronavirus cases

"We are writing to express serious concern about your company's failure to keep Walmart employees in Massachusetts safe amidst the coronavirus," 11 House and Senate Democrats wrote to Walmart CEO Doug McMillon Thursday in a letter obtained by CNN Business.

Worcester officials ordered a Walmart store to shut down last week after 23 employees tested positive for the virus, according to the local health department. All of the store's employees were later tested for the virus, and an additional 58 tested positive. The store, which tested 391 employees total, has since reopened.

"Massachusetts is suffering from a high rate of coronavirus cases, and several of our stores located in some of the state's hot spots have also been hit hard by the pandemic," Walmart said in a statement.

The company added, "It may be impossible to track the source of anyone's infection, especially in some of these communities that have felt the devastating impact of the virus. That's why we are working in partnership with local health officials and are taking aggressive steps to help ensure the safety of our associates and customers."

The letter seeks to raise pressure on Walmart over its worker safety policies after reports of coronavirus cases among employees at several stores in the state.

The letter also pointed to a complaint that United for Respect, a workers' advocacy group, filed with the Occupational Safety and Hazard Administration claiming that Walmart is "not regularly informing employees when a co-worker is diagnosed," not closing stores for cleaning and disinfecting after coronavirus cases have been diagnosed, and "not enforcing social distancing in stores that can have up to 900 customers in them at a time."

"These outbreaks occurred in the context of multiple worker-reported safety concerns at Walmart stores," the letter said.

Walmart declined to comment on the details of the United for Respect complaint. The retailer, which is the largest private employer in the United States, has more than 1.5 million workers in this country.

Like other retailers, the company is grappling with how to keep its doors open while keeping workers safe. It has implemented measures such as providing masks to employees, taking workers' temperatures, limiting the number of customers in stores and adding social distancing markers. But worker advocates have said the moves haven't been enough to protect employees.

In Quincy, Massachusetts, 11 employees tested positive for coronavirus and one employee died, according to Quincy health department commissioner Ruth Jones. Walmart closed the store this week after the health department contacted the company.

Jones said in an interview with CNN Business that employees had complained to her office that it "wasn't a safe place to work."

"We were getting complaints about the store not using social distancing and crowd control," Jones said.

Walmart declined to comment on what Jones told CNN Business.

Walmart also shut down two other stores in Massachusetts voluntarily for cleaning this week.

Separately, in Aurora, Colorado, public health officials briefly ordered a Walmart supercenter to shut down last month after a 72-year-old Walmart worker, her 63-year-old husband, and a 69-year-old third-party security contractor for the company died from coronavirus.

The local public health department there briefly ordered the store to shut down in part because of complaints of "lack of social distancing" and "too many people in the store at one time." The department has since allowed the store to reopen and said it has "good safety and health measures in place."