Staff working on the government's Universal Credit benefits system are being balloted for strikes in a dispute over workloads and recruitment, saying that they had been treated "with contempt".
Members of the Public and Commercial Services union at sites in Wolverhampton and Walsall are voting on whether to launch a campaign of industrial action.
The union said the service could face its first strike in March if there is a yes vote.
PCS general secretary Mark Serwotka said: "The possibility of a strike by Universal Credit staff should serve as a wake-up call to ministers who have repeatedly insisted Universal Credit is working well for workers and claimants when the opposite is in fact the case.
"Our members have not taken the decision to ballot lightly but the responsibility for the breakdown in industrial relations lies squarely with the Government who want to run this service into the ground while treating staff with contempt."
'We are disappointed'
The union is calling for the recruitment of more staff, permanent contracts for fixed-term employees and a cut in workloads.
A Department for Work and Pensions spokesman said: "We are disappointed that PCS has chosen to take this course of action and planned meetings with the union are ongoing.
"Our top priority remains assessing and making payments to customers.
"We are comfortable with current staffing levels and will monitor and reallocate resource where necessary."