The workers at sites in West Yorkshire and Cheshire claim to be losing £500 each through the company’s plan to reduce how much it puts into their pension pot while workers pay more.
Unite also claims Morrisons is ditching a long service pay award and increasing the speed at which goods are expected to be processed in warehouses.
Unite’s general secretary, Sharon Graham, at the time the changes were announced last November said the supermarket was “planning to fleece workers”.