Unite is to ballot up to 2,000 members at Fujitsu on industrial action over pay and pensions.
According to the union, around 4,000 employees are affected by the company's plans to close its final salary pension scheme.
If the proposal goes ahead, the company intends to dismiss employees after the end of the consultation period in September and offer them employment on new contracts which are unchanged except in relation to pensions, Unite said.
The union estimated that the proposed pension scheme change would reduce the total pay package of each employee by at least 15%.
Peter Skyte, Unite national officer for IT and communications, said, "Fujitsu Services is a highly profitable and successful company which is seeking to take advantage of the recession to attack pay, pensions and conditions.
In June, Unite called on the government to act quickly and decisively to safeguard the jobs and skills of hundreds of people working for Fujitsu on the £12.7bn National Programme for IT in the NHS.
Earlier this year Fujitsu hired pension law practice Wragge & Co to advise the company on a pension scheme that would be comparable to its existing final salary scheme.