More than 400 workers at Molson Coors brewery in Burton-on-Trent will be balloted for strike action in a row over pay and shift patterns.
Unite the Union claim 450 staff will be sacked after June 14, and then reinstated on lower pay and inferior terms & conditions.
It says some staff could lose up to £9,000 a year in the shake-up. Unite said that it had given the management seven days notice of the ballot which runs from 30 April to 28 May.
The brewery produces Carling, Grolsch, Coors Lite and Cobra lagers, as well as beers including Worthington, White Shield and Stones.