Yum Brands Inc.’s (YUM) subsidiary KFC said that it is working on limiting the use of antibiotics in the chicken it sells in the U.S. (See also: Jury Still Out on Yum Brands Split-Up.)

KFC is the last of the three biggest chicken chains in the U.S. to join the fight against the escalation of a group of antibiotic-resistant bacteria called superbugs. KFC is giving its chicken suppliers in the U.S. until the end of 2018 to cease the use of medically important antibiotics in raising their chickens, Reuters exclusively reported.

KFC U.S. President Kevin Hochman said the new antibiotic policy is only designed for KFC U.S. restaurants, which receive chicken supply from about 2,000 U.S. poultry farms, adding that KFC’s antibiotic policy is designed with a specific country in mind.

McDonalds Corp. (MCD) had announced in August 2016 that its 14,000 U.S. restaurants stopped selling chicken raised with antibiotics that are classified important to human medicine. McDonald’s had first announced this initiative in March 2015, setting a two-year target at the time.

The biggest chicken chain by sales in the U.S. Chick-fil-A was the first to announce its plan to stop serving poultry raised with antibiotics considered important to human medicine in 2014. Its goal is to make a full switch away from the controversial antibiotics by the end of 2019.

Yum Brands has been a target for activist organizations fighting the routine use of the controversial antibiotics in the chicken it serves. In January 2016, over 80 groups sent the CEO of Yum Brands a letter, saying the company should curtail the use of the controversial antibiotics and challenging it to make a public declaration about its position.

Yum responded, in 2016, by announcing that Taco Bell and Pizza Hut would stop serving poultry raised with the routine use of medically important antibiotics.