U.S. based sandwich restaurant chain Subway says it will make the switch to serving chicken raised without antibiotics that are also used in human medicine by 2016.

The company, according to a Nation’s Restaurant News report, added that it is also looking at antibiotic-free options for turkey, pork and other meats it serves. However, it has not given any timeline on when those changes will be made, citing challenges with finding enough suppliers to meet the chain’s needs.

Subway is making the changes after receiving pressure to reduce or eliminate sales of meat from livestock and poultry raised with antibiotics. In June, the company’s president and CEO, Frederick DeLuca, received a letter signed by representatives from 60 groups seeking an end to antibiotic use.

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As public concerns grow about how animal antibiotic use might play a role in antibiotic resistance, a number of major chain restaurants have adopted or are adopting policies eliminating or reducing the use of meats from animals raised with antibiotics.

McDonald’s in March announced that it would phase out the use of chicken meat from birds raised with medically important antibiotics. In 2014, Chick-fil-A announced that it would exclusively sell chicken raised without antibiotics within five years. Other major restaurant chains to adopt antibiotic-free policies concerning the meats it sells in its restaurants include Chipotle and Panera Bread.

Subway has more than 44,000 restaurants in 110 countries. More than 27,000 of those restaurants are located in the U.S.