CHICAGO - Several major U.S. meat plants run by JBS USA were not operating on Tuesday after the company reported a cyber attack over the weekend, according to company Facebook posts and unions.

Two kill and fabrication shifts had been canceled at JBS's beef plant in Greeley, Colorado, representatives of the United Food and Commercial Workers International Union Local 7 said in an e-mail. JBS Beef in Cactus, Texas, also said on Facebook it would not run on Tuesday -- updating an earlier post that had said the plant would run as normal.

A JBS pork plant in Ottumwa, Iowa, is not slaughtering, according to a local company Facebook post. JBS representatives did not immediately respond to questions about the attack, which shut down operations in Australia on Monday.

  - Reuters