About 130 jobs look set to be lost with the closure of a factory in Denbighshire.
Honeywell said it had started talks with staff about closing its site at St Asaph which manufactures plastic conduits and switches under the brand MK.
Work is set to be moved to some of the company's other sites in the UK and abroad, it said.
One union official said the news had come "completely out of the blue".
USA-based Honeywell employs 110,000 people around the globe.
Agency staff are also based at the St Asaph factory, but the total numbers of workers are not known.
A company statement said: "Honeywell is proposing to transfer all activities from the St Asaph site due to a need to consolidate core manufacturing processes in fewer locations.
"Unfortunately, we realise this affects valued employees and we are committed to open communication throughout the consultation period."
Vale of Clwyd MP Chris Ruane said it was "terrible news" for staff.
The Unite union's Wales regional secretary Peter Hughes said Honeywell's decision was a "huge blow to their exceptional workforce and the wider economy of north Wales".
"This decision has come completely out of the blue, with no prior consultation or discussion with Unite and the workforce," he added.
"Honeywell employees who went to work yesterday thinking they had a secure job and income for their families, have today had their futures thrown into complete disarray."