There are new concerns over a Swansea car plant which has confirmed 230 jobs are moving to Bridgend.
A new engine line is due to be added at the Bridgend plant
The T&G union claims Ford is "engineering the closure" of the Visteon factory, on Fabian Way.
Ford said the production jobs would transfer to its Bridgend engine plant by the end of March, following the switch of 90 other jobs in January.
Visteon said it needed extra capacity and there were no job losses associated with the changes.
Union regional secretary Andy Richards was part of a delegation which included Welsh Secretary Peter Hain who met senior managers at Visteon last month.
At the time Visteon said it was "facing a difficult business situation" and said about 100 workers would be moved.
"Lack of work"
Initially there were reports on Friday that that figure had been revised to 170, but the company later said in fact it was around 230.
Union leaders and politicians visited Visteon in Swansea last month
"We are calling on Visteon to bring forward a sustainable business plan for the Swansea site," said Mr Richards.
He pledged that the union would take its fight "to whatever levels we must".
Ford Bridgend and Visteon Swansea said the new Bridgend jobs would be mostly on assembly lines, building new hi-tech petrol engines for Ford, Jaguar and Land Rover vehicles.
They said a second "premium engine" was due to be added this year to Bridgend's new Premier Automotive Group line, which comprises Ford luxury brands such as Jaguar and Land Rover.
Visteon UK Ltd said its major customer needed more brake products than could be produced at Swansea.
In a statement, Visteon said: "Through this process of our customer securing additional capacity, no jobs have transferred to other companies and there are no job losses associated with this action".
Visteon also said the situation on its UK operations remained the same as the unions had been told in January, when they discussed the "serious business situation".
The company said it would meet union leaders soon "to clarify its position".