More than 1,100 jobs are feared to be at risk at Ford after the car giant revealed concerns over a slowdown in work for its Bridgend engine plant.
Ford is meeting with unions and staff as a leaked report reportedly showed it could be looking to cut up to 1,160 jobs at the plant in south Wales, leaving it with 600 workers at the site.
The company remained tight-lipped on the number of jobs at risk, but admitted "efficiencies" were high on the agenda.
A spokesman said a five-year plan showed "healthy volumes to occupy the current workforce over the next two to three years", but added: "Beyond that, identified workload is reduced and whilst such a forecast is not unusual, given the cyclical nature of our business, it is a concern."
Prime Minister Theresa May told MPs the Government had held talks with Ford over ways to help ensure the "success" of the firm's UK operations.
Speaking at Prime Minister's Questions, she said: "Ford is an important investor here, it's been established here for over a hundred years. We now account for around a third of Ford's global engine production and Bridgend continues to be an important part of that.
"We have had dialogue with Ford, we will continue to have a regular dialogue with Ford about the ways in which government can help to make sure that this success continues."
It is understood that Ford has projected the job losses based on the assumption that it is unable to bring in any new work at the plant.
Ford said it has proposed a joint working party with unions Unite and GMB "to identify future business opportunities".
A spokesman for the firm said: "It goes without saying, that in order to attract new business, the Bridgend operation would need to ensure its competitiveness, and addressing some of the current concerns relating to the plant's efficiency would be high on the agenda."
Trade union Unite said it would "defend the future of the Bridgend plant with all our might".
The GMB union said meetings with Ford had confirmed the "worst case scenario" that more than 1,100 jobs are under threat at Bridgend over the next five years.
Jeff Beck, GMB organiser, said: "This is a real kick in the teeth for our hard-working members at the Ford plant, as well as their families and the community as a whole."
He added: "Our first priority is to defend our members' jobs.
"We will be consulting with them to decide what action we will take in the wake of this devastating news."
Ford first announced cutbacks on its planned investment in the new Dragon engine in September last year.
The group had hoped to be producing 25,000 of the new petrol engines a year at the plant under plans first announced in 2015.