The Meat Workers Union says freezing workers at the Mataura works will lose pay of up to $400 per week if they accept a company move to upgrade the plant.
The Alliance Group says it will spend up to $27 million on the sheep and cattle processing plant but only if the 800 workers acccept new contracts.
Gary Davis from the New Zealand Meat Workers Union says the offer will cut 10 - 30% from workers' wages, meaning pay cuts of hundreds of dollars for top workers.
He says talks with the company about the contract will continue next week.