Union leaders say Ford will close its engine plant in Bridgend by September 2020.
A formal announcement will be made later, sparking fears for hundreds of jobs which are reliant on the factory.
Unite warned that the closure of Bridgend would send shockwaves through the Welsh economy and wider supply chain, imperilling the livelihoods of thousands of people.
Bridgend makes the Dragon petrol engine which is used in a range of Ford models across the globe.
Commenting Unite assistant general secretary Steve Turner said: “Ford will be taking an economic sledgehammer to the Welsh economy in an act of gross industrial sabotage if it doesn’t urgently reverse these closure plans.
“Instead of betraying workers who have worked tirelessly to make Bridgend one of the most efficient engine plants in the world, Ford bosses should be rebalancing global engine production from Mexico and India to Bridgend. There is a global yearly market of some 500,000 for the Dragon engine and we demand our fair share of that.
“The UK is Ford’s biggest European market, it holds first and second place in UK car sales yet disgracefully doesn’t produce a single vehicle here. If Ford wants to sell vehicles in this country it has a responsibility to maintain a strong manufacturing footprint here not run off into the sunset to cheaper markets where sales are low but profits high.
“Unite representatives across all of Ford’s UK sites have previously stated if any plant in the UK is faced with closure or compulsory redundancies that they would all move to a ballot for industrial action.
“Ford bosses should be in no doubt. Unite will not stand back and let Ford turn its back on its loyal UK workforce and allow our members’ livelihoods to be shredded because they are cheaper and easier to fire than their counterparts elsewhere in the world.
“In the coming days Unite will be consulting with our members across all of Ford’s UK sites on our next steps. We will also be working with the Welsh government and calling on UK ministers to step in to bring pressure to bear to make Ford rethink these disastrous closure plans.”
Carwyn Jones has tweeted following news about the future of the plant. This is what he has said:
Sadly it's been confirmed to me that Ford intend to shut the engine plant by next September. No reason given as to why it should be Bridgend. The workers deserve so much better than this after all their efforts and hard work. They did all that was asked of them— Carwyn Jones AM/AC (@AMCarwyn) June 6, 2019