Consumer groups will deliver a petition from more than 350,000 people to the KFC restaurant chain on Wednesday, calling on the Yum Brands Inc unit (YUM.N) to stop the routine use of antibiotics by the companies that supply its chicken.

Several fast-food restaurants, which have been under fire for selling unhealthy meals, are assuming the role of public health change agent by forcing their respective meat suppliers to adopt new practices aimed at keeping vital antibiotics working.

KFC has said that by 2017, antibiotics important to human medicine will only be used to maintain chicken health and only under the supervision and prescription of a licensed veterinarian. But critics say that policy effectively allows for routine use of antibiotics by its chicken suppliers.

As per federal government guidance, KFC does not allow the use of such antibiotics for growth promotion. Medical experts warn that the routine use of antibiotics to promote growth and prevent illness in healthy farm animals contributes to the rise of drug-resistant "superbug" infections that kill at least 23,000 Americans each year and represent a "catastrophic threat" to global health.

More than 70 percent of medically important antibiotics in the United States are sold for use on livestock and poultry.

McDonald's Corp (MCD.N) last week said it switched to chicken raised without antibiotics important to human health, months ahead of schedule.

Chick-fil-A Inc, which has surpassed KFC to become the No. 1 U.S. fast-food chicken chain by revenue, has vowed to fully transition to chicken raised without any antibiotics by the end of 2019.

KFC 'LAGGING'

"KFC is lagging woefully behind. Diners around the country want KFC to step up," said Lena Brook, food policy advocate with the Natural Resources Defense Council (NRDC), one of the groups delivering petitions to KFC's headquarters in Louisville, Kentucky.

KFC spokeswoman Kasey Mathes said on Wednesday the company was reviewing its position on antibiotics to determine the viability for its suppliers to go beyond the FDA guidelines for antibiotics usage.