The U.S. Department of Agriculture, or USDA, is threatening to shut down three poultry farms in California following an outbreak of salmonella across the nation that has resulted in nearly 300 people in 17 states becoming sick, according to reports.

Los Angeles Times reported that the USDA sent a letter to Foster Farms, one of the country's largest privately-owned poultry producers, pointing out that poor sanitary conditions at the facilities were a "serious ongoing threat to public health," and asked the poultry company to come up with a plan by Thursday to clean up its plants.

Two of the poultry plants are in Fresno and one is in Livingston, Calif., where the company is based.

The USDA issued a health alert on Monday after it detected strains of salmonella heidelberg in products from these three facilities. And, on Tuesday, the Centers for Disease Control and Prevention reported that 42 percent of people who fell sick across the country were hospitalized, and that 77 percent of those were from California.

The salmonella strains were resisting antibiotics according to the CDC report, and the outbreak has prompted organizations such as Consumer Reports, which regularly tests meat and poultry, to seek a recall of Foster Farms products.

"It is outrageous that Foster Farms has not issued a recall in the face of so many illnesses associated with their product," Urvashi Rangan, toxicologist and executive director of the organization’s food safety center, told LA Times. "We are calling on Foster Farms and the retail outlets that sell Foster Farms to recall the chicken processed at these plants. Foster Farms has a responsibility to public health to take this step."

According to LA Times, grocery chain Kroger is pulling chicken sourced from the three Foster Farms plants off its shelves.

"Those include fresh products, which would be like whole fryers, breasts, drums, thighs and ground chicken," Kendra Doyel, a spokeswoman for Ralphs, which is operated by Kroger, told LA Times. "It would not include cooked or processed products like lunch meat [and] hot dogs."

Reacting to the news, Foster Farms president Ron Foster said in a message on the company’s website apologizing for “any foodborne illness associated with Foster Farms chicken and for any concern this may have caused you.” He added that Foster Farms has brought in national food safety experts to assess the processes at its facilities to ensure there was no future cause for concern.