The European aerospace and defence giant Airbus would reconsider investment in the UK in the event of Britain leaving the European Union.
Paul Kahn, president of the 16,000-employee Airbus UK, said Britain must compete for international investment.
"The best way to guarantee this is by remaining part of the EU," he said.
Prime Minister David Cameron has promised a referendum on the UK's EU membership by the end of 2017, and the matter has been rising up the political and business agenda.
On Monday, the chairman of construction equipment firm JCB said the UK should not fear an exit from the EU.
And on Wednesday, the president of the CBI, Sir Mike Rake, said businesses should "speak out early" in favour of remaining in a reformed EU.
Mr Kahn said that with a UK referendum on leaving the EU perhaps less than 18 months away, companies like Airbus needed to be at the forefront of the debate.
"I believe that it is vital for a company such as Airbus to come out and make a stand in favour of Britain remaining in the European Union," he said.
Airbus employs 6,000 people at its site at Broughton, north Wales, where it assembles the wings for all Airbus aircraft. Several thousand more people are employed at Filton, near Bristol, designing wings and testing landing gear.
Mr Kahn stressed that if Britain were to leave the EU, the company would not suddenly close.
But he added: "If after an exit from the European Union, economic conditions in Britain were less favourable for business than in other parts of Europe, or beyond, would Airbus reconsider future investment in the United Kingdom? Yes, absolutely."
If Britain were to leave the EU Mr Kahn suggested the company could face more red tape in areas such as work visas and trade barriers.
He said he was not "blindly supporting Britain's membership of the EU", adding: "I welcome the UK government's intentions to deliver positive and hoped-for reforms - which would create a leaner and more efficient EU."
His comments came on the day that Mr Osborne told business leaders at the CBI that the government would be fighting for a reformed Europe.
courtesy of: BBC News