Almost 1,000 pension workers at Capita are to stage a 24-hour strike in a dispute over pay.
Members of Unite will walk out on Thursday, which the union said would cause disruption to the outsourcing company's blue chip clients.
National officer Dominic Hook said: "Our members are fed up to the back teeth by enduring poverty pay, while Capita accrues large profits on the back of their hard work.
"The strike will hit the services to a number of blue chip companies which may wish to put pressure on Capita bosses to come to a fair settlement.
"If Capita does not enter into constructive talks, more strikes are definitely on the cards, given the depth of anger of our members."
The Capita workers are based in Belfast, Birmingham, Bristol, Bournemouth, Glasgow, Manchester, Reading and Stirling.
The union claims a "derisory" pay offer would result in a real terms pay cut for 75% of staff.