An announcement on the proposed closure of Ford’s Bridgend plant will be made on Thursday, the BBC has been told.
Ford Europe and bosses from the United States will meet union leaders at its Essex headquarters.
The GMB said closure would “mean disaster” for the plant, which opened in 1980 and employs 1,700 workers.
Ford said it would not comment on speculation and Welsh Secretary Alun Cairns said he was in ongoing dialogue with the company.
It comes just months after Ford said it was cutting its Welsh workforce by 1,000, with 370 going in a first phase.
Investment in the new Dragon engine was scaled back, while production of an engine for Jaguar Land Rover is due to end this year.
There has already been concern about whether the plant would be viable making only 125,000 Dragon petrol engines a year.
It comes just days after car sales in the UK fell again and the BBC expects Ford will be in touch with Welsh Government ministers first thing in the morning.
It is understood the meeting has been called in the past 24 hours and senior managers from Ford in the United States will be present, as well as union leaders from the company’s other UK sites.
GMB regional organiser Jeff Beck said: “We haven’t had any confirmation of any closure, but we’re meeting with Ford tomorrow and a new agenda has been arranged, which we’re yet to see.
“If our worst fears are confirmed, it will mean disaster for both our members in Bridgend and the community at large.”
Bridgend AM and former First Minister Carwyn Jones admitted this was a “worrying time” for workers.
Plaid Cymru leader Adam Price said closure would be “one of the most bitter blows” for the Welsh economy for more than 30 years.
“Ford is the jewel in the crown of the car industry – which is the hardcore of our manufacturing sector – so the implications of this in terms of the supply chain in terms of job losses is very, very grave indeed.”
Media playback is unsupported on your device
Mr Cairns said he had been in touch with Welsh Economy Minister Ken Skates and said the automotive sector was going through a period of structural change towards electric vehicles.
“We’re determined to do what we can to protect the future employment in that area in this exciting sector,” he added.
Mr Skates has told AMs he is seeking urgent talks with Ford over the “speculation”.
Timeline
2008: Ford announces it will operate as a single global company – meaning its Bridgend engine plant had to compete with the firm’s other factories across the world, not just in Europe
2015: Bridgend secures investment for Dragon petrol engine project – with 250,000 engines a year, although it has capacity for 750,000 a year
2016: The planned Dragon investment is reduced to £121m and the number of engines is cut in half to 125,000
2017: Ford projects a reduction of 1,160 workers by 2021 and confirms production of Jaguar Land Rover engines – which involves half the workforce – will end in 2020
2018: Workers making Jaguar engines face a five-day shutdown as a knock-on effect from JLR’s temporary production halt. Ford’s European boss warns a no-deal Brexit would be a “pretty disastrous”
2019: Ford plans to cut 370 jobs the first phase of redundancies which will total 990 by 2021. The Dragon project is scheduled to employ about 500