Hundreds of workers at a coffee processing plant will be sacked and then reemployed on inferior pay and conditions, a union has claimed.
Unite said 300 staff at the Jacobs Douwe Egberts (JDE) plant in Banbury, Oxfordshire, have been given notices without any consultation.
It claimed JDE had employed "strong-arm tactics".
The company said "modernisation" at the plant is "essential" and no jobs would be lost.
JDE, which makes Kenco Tassimo and Millicano at the plant, said any changes would be subject to "full and thorough consultation" with the union.
Unite said talks have been "adjourned" and not fully broken down.
Joe Clarke, its national officer for the food industry, said: "In nearly 30 years of union work I have never encountered such a negative approach from an employer to ignore the established consultation and negotiating procedures.
"It has come like a bolt out of the blue.
"We will not stand by and see our members' livelihoods destroyed and the collateral damage to the local Banbury economy and social fabric.
"The campaign now moves into top gear."
Rob Williams, JDE's plant director, said: "We have been proudly making coffee at Banbury for 55 years and want to continue to do so.
"We can confirm that we are considering making some changes to the way we work at Banbury.
"Many of our shift patterns and processes have not changed in decades which means some modernisation is essential if we are to ensure coffee manufacturing stays in Banbury for years to come.
"The proposed changes do not include a reduction in headcount."