Members of the GMB union at Forterra's Newbury site are to vote on whether to strike over a pay gap within the company.
They say that they are being paid as much as 20% less than colleagues at another Forterra site for doing the same job, despite management assurances last year that the company would work towards closing the gap.
The GMB held a consultative ballot following Forterra's 2018 pay offer, which it says fails to address the issue of pay parity between different sites, and members supported a full formal ballot for strike action.
The ballot opens tomorrow and the results are expected on 6 December.
The union secured recognition at the heavy building materials supplier's Newbury site in August 2017. It has been negotiating with managers since then to narrow the pay gap with another Forterra site that has had union recognition for a longer period.
It claims that its members in Newbury are under-paid between 3% and more than 20% for doing the same jobs carried out on another site, despite having a higher cost of living.
Asia Allison, GMB Regional Organiser, said:"During 2017 pay negotiations, Forterra management committed to narrowing the pay gap between two Forterra sites. Unfortunately, they have failed to deliver this in the 2018 pay round. GMB members are furious and morale is plunging as a result of management's worthless commitments that they have no intention of fulfilling.
"The fact that our members voted by almost 100% for strike action in a consultative ballot shows the depth of anger and frustration they feel at the outrageous attitude adopted by this profitable company.
"GMB members are now calling on directors to address the pay parity and bring their pay in line with the other site. They are demanding a formal deal ‘stamped’ and will not settle any more for management's empty promises.
"Management's refusal to deal with the pay issue have been left us with no other option, except to ballot GMB members for industrial action."
Forterra declined to comment.