HGV drivers and shunters at the Müller Stonehouse factory, members of Unite the union, will escalate their dispute over imposed rota changes with 11 days of all-out strike action.
Around 70 workers will strike from 19th-29th October.
The employer is seeking to impose a change to a five-days-on, two-days-off rota system to require all drivers to work at least one day every weekend.
The move is seen as a breach of an agreement the company signed with Unite earlier this year.
The workers are responsible for delivering milk and other dairy products to Marks & Spencer and Waitrose nationwide.
Unite general secretary Sharon Graham said: “It’s very simple; Müller signed an agreement with our members and they should stick to it.
“Unite will not accept attacks on our members’ jobs, pay or conditions. Müllers’ Gloucestershire workforce has the union’s full backing in this dispute.”
Unite regional officer Amy Roberts said: “Müller needs to abide by the agreement it signed and drop these rota changes, which will negatively impact our members’ quality of life.”
A spokesperson for Müller Milk and Ingredients said: “These rota changes were implemented following consultation and agreement with joint trade unions last year.
“The agreement aims to transition those on legacy five days working / three days off patterns to align with the five days working / two days off pattern which most full-time employees in the UK are familiar with.
“Following the introduction of the rota changes, which are not related to pay, a small number of logistics employees at our Severnside site voted in favour of industrial action.
“It is important to stress that we have thorough plans in place to ensure deliveries of dairy products to our customers will not be affected.”