Car giant Ford has warned that leaving the European Union without a deal next month would be "catastrophic" for the UK's auto industry.
The company did not confirm a newspaper report that it was stepping up preparations to move production out of the UK.
A Ford spokesman said: "We have long urged the UK Government and Parliament to work together to avoid the country leaving the EU on a no-deal, hard-Brexit basis on March 29.
"Such a situation would be catastrophic for the UK auto industry and Ford's manufacturing operations in the country.
"We will take whatever action is necessary to preserve the competitiveness of our European business."
The Times said Ford told Prime Minister Theresa May during a telephone call with business leaders that it was preparing alternative sites abroad.
The car industry has been warning about the impact of a no-deal Brexit, with some already cutting back on jobs and production plans.
Nissan said last week it would no longer build its X-Trail car in Sunderland, Jaguar Land Rover has announced plans to cut 4,500 jobs in the UK and Ford could cut about 1,000 jobs, mainly at its Bridgend engine plant.
Unite national officer Des Quinn said: "This latest warning from Ford underlines the catastrophic consequences of a no-deal Brexit on the UK's world leading car industry, its integrated supply chain and wider manufacturing communities.
"Ministers and MPs must stop gambling with the futures of UK workers and their families.
"They now must do what is best for the country by taking a no deal, hard Brexit off the table and securing the tariff-free, frictionless trade with Europe through a permanent customs union on which our manufacturing success depends."