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 plant employs 1,700 workers from across south Wales and the GMB union said closure would "mean disaster".
Ford said it would not comment on speculation but workers arriving at the plant for Thursday's early shift said they feared the worst.
Tony Phillips, who has been at the plant for 31 years, said: "I'm expecting to lose my job this morning."
Fellow worker Mark Lendrum said he was "devastated" by the speculation, adding: "South Wales is going to be like a ghost town."
Welsh Secretary Alun Cairns said he was in ongoing dialogue with the company.
It comes just months after Ford said it was , 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 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: "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 said: "Nobody would have thought before yesterday that this plant would close completely.
"Yes, there were challenges in terms of jobs, but there were also opportunities," he told BBC Radio Wales .
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."
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".
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
2018: Workers making Jaguar engines face a five-day shutdown as a Ford's European boss warns a
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