The USDA says that Foster Farms has until Thursday to tell them how they plan to fix the problem. If that deadline's not met, they will withhold inspections, which will effectively shut the plants down.
While the cases were first reported in March, Los Angeles County health officials now say they've got 18 confirmed cases of the same strain of salmonella.
In Orange County, 15 residents reported being sick; seven of them were hospitalized. Ventura County health officials say they got nine cases.
Nearly 300 people in 18 states were sickened after eating chicken that the USDA believes came from Foster Farms. Forty-two percent of those people were hospitalized.
"I was talking to the CDC about this last night and this is one of those outbreaks they're worried about. The reason is the number of people hospitalized by the salmonella is higher than they would expect. And the strains of the organism, many of them are resistant to antibiotics," said Dr. Richard Besser, ABC News' chief health and medical editor.
The concern is so serious, the Centers for Disease Control and Prevention is bringing back workers furloughed in the government shutdown to respond. They're worried more people could still get sick.
The USDA has not directly linked the outbreak of illnesses to a specific product or production period. The USDA mark on suspect packages would read: P6137, P6137A and P7632.
Foster Farms says they are working to address the problem but are not issuing a recall.
The company released a statement on Wednesday saying, "Foster Farms is dedicated to resolving any concerns by the USDA. We are fully cooperating with FSIS during this process and are responding with new and already implemented practices in the affected plants. Some of these interventions have been in place for nearly two months and are proving to be successful. In addition, we have brought in national food safety experts to assess our processes."
Foster Farms says on its website that its "products are safe to consume if properly handled and fully cooked."
Even though the meat hasn't been recalled, some grocery stores are taking it off their shelves anyway. Kroger Co. said it is taking some Foster Farms products from the shelves in certain stores and calling customers who it knows may have purchased the products. The company owns several chains, including Ralph's, Fred Meyer, Fry's and others.
Salmonella is a pathogen that contaminates meat during slaughter and processing, and is especially common in raw chicken. Symptoms include fever, nausea, cramps and diarrhea.
Tips to help prevent salmonella sickness
Food safety experts say be sure you wash your hands with soap and warm water before and after handling raw chicken.
Cook chicken to 165 degrees; that will kill the bacteria. The only way to know is to check with a thermometer.
Food safety specialist Jeff Nelken says never wash or rinse raw chicken.
"We recommend that you not wash raw chicken, because the likelihood of splashing salmonella all around your kitchen is much greater," said Nelken.
Another helpful tip is to use color-coded cutting boards and utensils to prevent cross contamination.
Remember to wipe down the area -- a little bleach, diluted with water, is all it takes.
The Associated Press contributed to this report.