Nissan boss Carlos Ghosn has said the Japanese car maker would "reconsider" its future in the UK if it left the European Union.
The chief executive was speaking at the launch of Nissan's new Qashqai model, which will be built at Nissan's Sunderland site, where the motoring company employs 6,500 workers.
Ghosn told the BBC: "If anything has to change we (would) need to reconsider our strategy and our investments for the future."
He did however add that he considered such an exit unlikely.
Prime Minister David Cameron has promised a vote on EU membership in 2017 if the Conservatives win the next general election in 2015.
"Obviously it's going to be a major factor happening and we are going to need to consider what does it mean for us for the future," Ghosn said.
"I'm not worried about Sunderland. Sunderland is a very competitive plant, it's a very productive plant and it's a European plant based in the UK."
John Mills, co-chairman of the Business for Britain group, which is seeking reform of the UK's EU membership, told BBC Radio 4's Today programme: "If Britain were to leave the EU - and that's not what Business for Britain is advocating - I think that Nissan and any other car company would have to take a view as to what the prospects were, particularly if we continue to have free trade with Europe, which is very likely to happen.
"What we are saying is that if there's renegotiation then a much larger proportion of British business would want to stay in. I think Mr Ghosn would be wise to support what we say, which is to push for these negotiations to be successfully accomplished."