Unions say Airbus supplier Magellan Aerospace has told workers 240 jobs are under threat at sites in Wrexham and Deeside.
The company - which employs around 500 workers in North Wales - recently warned operations are under review after the worst crisis in aviation "since 9/11".
Today Unite said it had been informed that 240 roles are at risk.
Canadian firm Magellan has been asked to comment.
Peter Hughes, Unite Wales regional secretary, said: “Today’s announcement by Magellan is devastating news for the workforce at the plant. The proposed scale of these redundancies would affect almost half of the current employees. The potential economic consequences for the economy of north east Wales are huge.
"Whilst Unite recognises that there is intense pressure on the aerospace sector at present, it is crucial that Magellan is in a position to pick up production levels quickly once the pandemic and its effect on the sector eases.
"If Magellan loses almost half of its highly skilled workforce, then bouncing back in a post=Brexit economy becomes extremely difficult."
He added: "Unite will be doing everything possible to support our members during this difficult and worrying time."
