The world’s largest meat producer, JBS, has been forced to shut down many of its slaughterhouses, including in the United States, due to a cyberattack on the company’s computer networks on Sunday, raising concerns about food security.

The Brazilian meat giant’s five biggest beef plants in the U.S., which handle over 20,000 cattle every day, have stopped meat processing, according to company Facebook posts, after an attack on its servers on Sunday. The company is the biggest producer of beef in the country, making up almost 25% of all beef capacity and almost one-fifth of pork being sold in the U.S., fueling concerns about a shortage of meat products and prices rising.