BAE Systems fears thousands of jobs could go in Lancashire and Greater Manchester as a result of expected defence spending cuts, the BBC has learned.
An internal BAE Systems document seen by the BBC shows BAE's concern that the Eurofighter project could end.
The Eurofighter Typhoon aircraft is partly built in Warton, which employs nearly 8,000 workers.
Jobs could go at Samlesbury if the Tornado service contract is scrapped.
The cuts could also see the bringing forward of the closure of the site at Woodford, in Greater Manchester, which is due to shut in 2012 with the end of Nimrod production.
BAE is worried about the government's commitment to the Joint Strike Fighter (JSF) project, which if axed would also mean redundancies, particularly at Samlesbury.
The JSF can gather information from space, land and other aircraft - and then transmit that information to commanders on the ground.
The aft fuselage for every plane produced is being built in Samlesbury, with 1,000 workers there involved, plus more defence-related contractors based in Manchester and Bolton.
Cheadle MP Mark Hunter said it would be "daft" to bring forward the closure of the Nimrod plant in Woodford, Greater Manchester, which employs 950 people on this project.
The plant is due to close in 2012 but Mr Hunter said: "It would be premature to do this as most of the money has already been spent."
The government is due to publish its Strategic Defence and Security Review (SDSR) on Tuesday afternoon.
The prime minister has already said the Ministry of Defence will face a cut of about 8% in its budget.
A spokesperson for BAE said: "We are fully aware of the pressures on public expenditure that the new government is facing and are committed to playing our part in supporting the SDSR in order to help identify cost effective means of achieving the government's defence objectives.
"As the outcome of the SDSR is not known it is not appropriate for us to comment further."