Brazil-based JBS, the world’s largest meat producer, has shuttered all of its US-based beef plants as of Tuesday while responding to a cyberattack,

The shutdowns impacted all nine beef plants, located in Arizona, Texas, Nebraska, Colorado, Wisconsin, Utah, Michigan and Pennsylvania, according to officials from the United Food and Commercial Workers (UFCW) International Union, which represents more than 25,000 JBS employees. JBS’s US-based pork plants are still operational.

The shuttered plants produce nearly one-quarter of U.S. beef supplies. In total, JBS employs more than 66,000 workers across 84 US-based locations.

The attack raised concerns of a potential meat shortage in the U.S. and several other countries impacted by the situation. It wasn’t immediately clear how the shutdown would affect meat prices.

JBS did not immediately respond to a request for comment. Bloomberg was first to report on the shutdowns.

JBS USA said it discovered on Sunday that an “organized cybersecurity attack” had impacted some of its computer systems in North America and Australia. The company noted it would “take time” to resolve the cybersecurity breach and warned it “may delay certain transactions with customers and suppliers.”

UFCW called on the company to pay workers impacted by the plant shutdowns.

“As the union for JBS meatpacking workers across the country, UFCW is pleased JBS is working around the clock to resolve this, and UFCW is urging JBS to ensure that all of its meatpacking workers receive their contractually guaranteed pay as these plant shutdowns continue,” UFCW International President Marc Perrone said in a statement.

JBS has yet to publicly disclose that it was targeted by a ransomware attack. The White House said it was aware of the situation and indicated a criminal group likely based in Russia was believed to be responsible.

“JBS notified the administration that the ransom demand came from a criminal organization likely based in Russia. The White House is engaging directly with the Russian government on this matter and delivering the message that responsible states do not harbor ransomware criminals,” White House principal deputy press secretary Karine Jean-Pierre said at a press briefing.