GREELEY, Colo. (AP) — Thousands of workers for the world’s largest meatpacking company began a two-week strike Monday in Colorado, threatening to make already costly beef even more expensive for U.S. consumers.

As the sun rose, employees picketed outside the Swift Beef Co. plant in Greeley, one of the largest slaughterhouses in the nation that’s owned by JBS USA. Walking back and forth in the morning cold, bundled in blankets, some yelled “huelga!” — Spanish for “strike.” Others waved signs encouraging people to not buy from JBS.

The first walkout at a U.S. beef slaughterhouse in four decades follows accusations from union officials that the company retaliated against workers and committed other unfair labor practices. They said the company offered wage increases of less than 2% annually, which is below Colorado’s inflation rate.

Union officials said 99% of the plant’s 3,800 unionized workers voted to strike. More than 2,600 showed up at the picket line by early Monday afternoon and others were expected to check in over coming days, said Claire Poundstone, an attorney for the United Food and Commercial Union Local 7.