With the number of salmonella illnesses linked to Foster Farms chicken climbing to more than 600 cases this month, two members of Congress introduced legislation Wednesday that would require food recalls in such circumstances.

The eight-month-long outbreak has spread to 27 states and Puerto Rico, with dozens of new cases emerging in recent weeks. The cases are connected to chicken processed in plants that are struggling to kill salmonella strains resistant to several classes of antibiotics, according to the U.S. Centers of Disease Control and Prevention.

The U.S. Department of Agriculture has issued a public health alert and overseen changes in Foster Farms’ processing lines, including the addition additional of new anti-bacterial sprays, but department officials said they do not have the authority to order a recall.

Foster Farms has declined to order a voluntary recall, saying it believes the chicken is safe if properly handled to prevent spread of the contamination and if cooked to 165 degrees.

On Wednesday, Rep. Rosa DeLauro (D-Conn.) and Rep. Louise M. Slaughter (D-N.Y.) , said consumers need better protections. They believe USDA officials have authority to order recalls when especially virulent bacterial strains are triggering outbreaks and said a new law is needed to make this happen.

“The USDA has failed to recall meat contaminated with antibiotic-resistant pathogens because they do not believe they have the legal authority to do so. This bill would ensure there is no confusion,” the two lawmakers said in a prepared statement. “We need federal agencies that will protect public health, not bend to the threats of deep-pocketed food producers seeking to escape regulation.”

The USDA said it has not yet taken a position on the bill, called the Pathogens Reduction and Testing Reform Act. It released this statement Wednesday: “We appreciate the Congresswomen’s ongoing efforts on our shared goal of ensuring food safety standards continue to be stringent, effective, and constantly improving. FSIS will continue to work aggressively in preventing foodborne illness, including implementing the first ever performance standards for Salmonella in chicken parts and ground poultry later this year.”

If enacted, the measure would require the USDA to recall meat, poultry and egg products contaminated by pathogens that cause serious illnesses or death and that are also resistant to two or more classes of antibiotics commonly used to treat human illnesses.

The ongoing outbreak, linked to Foster Farms, involves seven strains of salmonella Heidelberg that are resistant to several classes of commonly prescribed antibiotics, the CDC said. The agency said that though these antibiotics are not typically used to treat salmonella infections, antibiotic resistance can be associated with increased risk of hospitalization in those who become infected.

More than 40 percent of those who have been diagnosed with a salmonella infection linked to the Foster Farms outbreak have been hospitalized, according to the CDC. The agency also said it is the largest reported salmonella-related outbreak linked to chicken in the past three decades.

Foster Farms said it has spent $75 million in upgrades to reduce salmonella in recent months, with an emphasis on reducing the bacteria in chicken parts — breasts, thighs and wings — that have been implicated in the outbreak. Recent tests, the company said, show salmonella rates for the company’s chicken parts are at about 2 percent at the three plants tied to the outbreak. The industry standard is 25 percent. The USDA does not have a standard for chicken parts, but is in the process of determining what it should be.

DeLauro and Slaughter were joined Wednesday by several food safety advocacy groups that for years have been pushing for the USDA to label virulent salmonella strains as “adulterants,” which would ban products contaminated with them and therefore force a recall. The USDA has used this same approach with raw beef, declaring six E. coli strains that are antibiotic-resistent as adulterants. Over the past 15 years, as the USDA has instituted the bans, the rate of E.coli-related illnesses has plummeted while salmonella-related illness rates have remained constant.

In a prepared statement, USDA Food Safety and Inspection Service officials said it “continues to closely monitor the salmonella Heidelberg outbreak as well as the three Foster Farms facilities which have been identified by CDC as a likely source.”

The department also said it has increased salmonella testing at the plants, which has shown low levels of the bacteria, prompting them to investigate “whether illnesses are being caused by other sources.”