Workers at BAE Systems in Lancashire have said they urgently need assurances about the government's commitment to buy more planes.
Prime Minister David Cameron said the Eurofighter Typhoon jet and the Joint Strike Fighter aircraft would be at the heart of the Royal Air Force's future.
But it is not clear how many planes the government will order.
The Eurofighter Typhoon aircraft is partly built in Warton, where nearly 8,000 workers are employed.
BAE said it welcomed the government's commitment to two fighter jets and would work with officials to understand what it could mean for its business.
Phil Entwistle, from the Unite union at BAE's Samlesbury plant, said it was vital workers knew where they stood.
Mr Entwistle said the effect of any reduction in orders would have wider repercussions.
"The local communities, shops, Preston, Blackpool, Blackburn - you are talking more than 60 to 70,000 people who are associated with BAE Systems at the Warton Unit - and if there was an impact on JSF or Eurofighter you could see local communities going down the pan."
One worker told the BBC: "You just wonder what's going to happen, whether you are going to have job.
"There's a lot of people with young families I feel sorry for."