UK defence and aerospace group BAE Systems is to sell its 20% stake in European aircraft maker Airbus.
Broughton is now one of the largest factories in the UK
It is expected to be bought by EADS, the Franco-German group that owns the rest of Airbus, the BBC has learned.
Airbus employs 13,000 people in the UK, where it designs and builds wings for its fleet of large commercial jets.
The sale means there will no longer be any British ownership of the huge manufacturing sites at Broughton in North Wales and Filton near Bristol.
Airbus recently announced the creation of an extra 650 jobs at Broughton, which is Wales' biggest manufacturing site with 6,000 staff.
"There will inevitably be fears that, over time, the manufacturing capability and the high-skilled engineering jobs will leave the UK," said BBC business editor Robert Peston.
"The government will be seeking guarantees for the future of these jobs.
"They paid lots of subsidies over the years in the form of launch aid."
A BAE Systems spokesman said that the company had no comment to make at this stage.
Focus on the US
As well as the staff directly employed by Airbus in Britain, as many as 135,000 jobs at UK suppliers are thought to depend on it.
Union leaders said they would seeking urgent talks with BAE Systems and Airbus on their intentions for the UK sites.
"There will be tens of thousands of worried people," said Ian Wadell, the Amicus union's national officer for aerospace.
"Broughton is a hugely important employer for that part of Wales and Merseyside, it doesn't bear thinking about if the future of that site is under threat," he said.
"Filton is at the centre of a huge aerospace cluster in the South-West of England."
AIRBUS KEY FACTS
The first ever Airbus, an A300, took off in October 1974
British Aerospace joined the consortium in 1979
There are over 3,900 Airbus jets in service
Airbus employs a total of 55,000 staff Worldwide
Airbus turnover in 2005 was £15.3bn
Airbus sold a record 1,055 planes last year, giving it a larger share of new orders than US rival Boeing.
It is thought that BAE sees this as a good time to sell its stake, which could be worth up to £3bn ($5.25bn).
The company is expected to invest the proceeds in its rapidly growing US operations, where it produces 35% of its sales.
Despite a bumper year for Airbus sales in 2005, BAE's commercial aerospace division saw its overall profits fall to £179m from £201m a year earlier because of weak demand for its regional jets.
BAE's move towards concentrating on its defence operations was reflected by last year's acquisition of US firm United Defense for £2.1bn.