Workers employed by Atos, the French multinational company which runs a number of Government contracts, are to strike in a row over pay.
The Public and Commercial Services union said around 2,000 of its members who administer the Department for Work and Pensions medical examinations, work in National Savings, the Equitable Life compensation scheme and who deliver IT support for customers such as the BBC, will walk out tomorrow.
The union said Atos has offered staff who work in healthcare a 2% rise and those who work in IT services 2.8%, linked to changes to longstanding terms and conditions such as annual leave and flexible working arrangements.
An Atos spokesman said: "Robust contingency plans are in place to maintain services during industrial action.
"The changes we have put forward are in order to sustain our business for the future and we have made a fair and competitive offer which we believe is substantial in the current climate and are disappointed in this position.
"This strike action does not reflect the view of the vast majority of our employees."
The union warned that the strike was likely to be the first in a series of walkouts which will "seriously affect" the company's ability to meet Government service level agreements.
A work to rule will be held from November 6.
PCS general secretary Mark Serwotka said : "If the company can afford a 14% pay rise for its chief executive, it can afford to reward its low-paid, hard-working staff fairly.
"Our members are angry and determined. Like workers elsewhere they have seen the money in their pockets and purses reduce, whilst food costs, energy costs, transport costs soar. This must end.
"Our members are being asked to suffer austerity whilst the cream from the £1.6 billion Government contracts that Atos hold is skimmed off for the bosses and shareholders of this multinational company".
Atos pointed out that it is a living wage employer.