Engine maker Rolls-Royce has come under fire after admitting it is considering building a new hi-tech facility overseas rather than in the UK.
The company told workers it is looking at the feasibility of constructing an aircraft engine testing plant in Germany or the US instead of at its UK base in Derby, the Observer reported.
It is a further blow for Derby after train maker Bombardier announced 1,400 job losses in the city following the Government's announcement that it would award a £1.4 billion contract to Germany's Siemens.
Adrian Axtell, Unite regional secretary for the East Midlands, said: "This has potentially long-term implications for Derby's manufacturing base.
"Work follows the experimental test-beds and a significant number of jobs in Derby are linked to development projects.
"Rolls-Royce, with the support of the Government, need to do everything possible to maintain its development projects in Derby in the long term."
One trade union source said the announcement hit staff "like a ton of bricks" and exacerbated concerns about the future of manufacturing in the city in the wake of the Bombardier announcement.
Mr Axtell, who represents about half of Rolls Royce's 11,000-strong workforce in the city, added: "The uncertainties arising from Rolls-Royce's plans go to show why the Government should support Bombardier when it can instead of allowing the work to go to Germany."
Rolls said its Derby plant - its centre of excellence for large engines - will continue to build and test Trent XWB engines for the new Airbus A350 aircraft due to launch in 2013.
A spokesman for the firm, which employs 39,000 people and manufactures in 20 different countries, said the company will double the number of Trent engines it produces to power the next generation of wide body planes.
He added: "Rolls-Royce is investing billions of pounds, in the UK and around the world, so that it can keep up with customer demand and fulfil its £60 billion order book.
"This will sustain jobs at Rolls-Royce as well as in the hundreds of British companies in our supply chain."