More than 550 UK jobs are at risk after an automobile and industrial firm announced plans to close plants amid "uncertainty surrounding Brexit".
Schaeffler plants in Llanelli and Plymouth are earmarked for closure, with the firm proposing to relocate production to plants outside the UK.
It has started a 45-day consultation on the plans.
In Plymouth, 350 staff are employed in the factory and 220 are at the Llanelli plant.
The union Unite said it would "fight for every job".
Assistant general secretary Tony Burke called the closures "yet another body blow for the UK's automotive supply chain and the wider car industry".
He said it showed what was "in store if the UK crashes out of the European Union without a deal that secures tariff free frictionless trade"
The firm said: "The uncertainty surrounding Brexit was one factor amongst others in the analysis of the UK market."
Llanelli MP Nia Griffith said: "I am worried obviously about the affect on families in the area... and the possible knock-on affect on other local businesses.
"It is important to try to offer the company any help to try to persuade them to change their minds."
She said Llanelli AM Lee Waters had already been talking to the Welsh economy secretary Ken Skates to see what was possible.
Luke Pollard, MP for Plymouth Sutton, said the closure was "deeply worrying" and showed the "uncertainty of the hard Brexit".
"We need to be in a customs union, close to the single market or we will lose even more jobs," he added.
Johnny Mercer, the MP for Plymouth Moor View, said the closure was a "short-sighted mistake" by Schaeffler.
Speaking about the possible impact on Llanelli, Councillor Deryk Cundy who represents Bynea, said the loss of "well-paid" jobs would be a massive blow.
"It will also affect Carmarthenshire and wider. We will need to form a taskforce. [We need] to persuade Schaeffler to rethink their decision," he said.
Greig Littlefair, managing director of Schaeffler UK, said the firm wanted "transparent and fair discussions with the employees affected".
Schaeffler, which employs more than 1,000 people at five facilities in the UK, will not be closing its largest plant in Sheffield.
It is anticipated the UK reorganisation will take up to two years to implement.
Juergen Ziegler, regional CEO Europe at Schaeffler, said: "Brexit is clearly not the single decisive factor behind our decision-making for the UK market, but the need to plan for various complex scenarios has brought forward the timing."
The closures are part of the firm's "Agenda 4 plus One" reorganisation plan examining strategic and economic competitiveness and the long-term sustainability of facilities.