GREELEY, Colo. — About 3,800 workers at one of the nation’s largest meatpacking plants were set to strike Monday morning in Colorado in what union representatives said would be the first walkout at a U.S. beef slaughterhouse since the 1980s.

The strike at the Swift Beef Co. plant in Greeley was set to begin at 5:30 a.m. MDT, said Kim Cordova, president of United Food and Commercial Workers Local 7, which represents the workers.

It follows accusations from union officials that owner JBS USA retaliated against workers and committed other unfair labor practices amid contract negotiations. A previous contract was due to expire at midnight Sunday.

The expected strike comes at a 75-year low for the U.S. cattle population, with a Jan. 1 inventory of 86.2 million animals — down 1% from the prior year. Beef prices have added to economic anxiety in the U.S., while the administration of President Donald Trump has turned to a trade deal with Argentina in efforts to lower prices for food, including beef.

It also follows the January closure of a meatpacking plant in Lexington, Nebraska, which was expected to ripple through the local economy and community.

At the Greeley plant, the company tried to intimidate workers to quit the union in one-on-one meetings, union general counsel Matt Shechter said.

Cordova said 99% of workers voted to authorize the strike. No formal negotiations took place over the weekend after the company refused a union request to negotiate on Saturday, Shechter said.

JBS USA said in statement that any employee who didn’t want to strike would have work and be paid. The company said it would operate two shifts at the plant Monday and would temporarily move production as needed to other JBS facilities.

The statement said the company operates in full compliance with federal and state labor and employment laws.

“Our goal is to minimize impact to our customers, our partners, and the broader marketplace while we work toward a fair resolution in Greeley,” the company said.

It’s the first strike at a U.S. slaughterhouse since workers walked out at a Hormel plant in Minnesota in 1985, Cordova said. That strike lasted more than a year and included violent confrontations between police and protesters, according to the Minnesota Historical Society.