The computer giant Hewlett-Packard says it is cutting 1,124 posts in the UK as part of a global downsizing.
The US company says it will start the process next year.
The Unite union said it had attended a meeting where managers outlined their plans to cut jobs at the group's sites in Bracknell, Sheffield and Warrington.
Demand for HP's core desktop computers has slumped and it has struggled to adapt to consumers' preference for laptop and tablet devices.
Unite said more than 600 jobs could be lost at the Bracknell hub, almost 500 at Warrington and 23 at Sheffield.
Last year, HP, the world's largest maker of personal computers, said it would cut 27,000 jobs worldwide - about 8% of its then workforce - by the end of 2014.
HP said not all the 1,124 would leave the firm.
It said some people would get new roles within the company, as HP is hiring at the same time.
The company said it had a variety of plans to support workers affected by the changes: "HP remains committed to supporting the employability of its employees through a number of internal initiatives, including re-skilling, redeployment and support to obtain alternative employment as appropriate."
But Unite said it believed many in the workforce had lost faith in the company.
The union's national officer, Ian Tonks, said: "For the last five years, HP has been addicted to a culture of job cuts in the UK to such an extent that its highly skilled workforce has little faith in the way the company is being managed and will be, going forward.
"Unite will be doing everything possible to mitigate these job losses, which are a hammer blow to the UK's IT sector and very distressing for employees in the run-up to Christmas."
The company's latest profit report, released last week, showed its financial performance was improving.
Although fourth-quarter revenue fell 3% to $29.1bn (£18bn), that was about half the size of the fall expected, while revenue at the key enterprise group rose and income was $2bn.
The results suggested its enterprise division would make up for falling PC sales.
Chief executive Meg Whitman said the results showed that HP's turnaround remained on track.