A senior director of Siemens has warned it would be harder to negotiate factory investment in the UK if Britain left the European Union.
Juergen Maier, managing director of Siemens' UK and Ireland Industry Sector, told a national newspaper business debate that such a move would be disastrous for British manufacturers.
Siemens has invested heavily in Lincolnshire, with factories in Lincoln and at Teal Park nearby and employs 13,000 people across the country.
Mr Maier reportedly said it is already tough enough to convince the board in Germany to invest in the UK for manufacturing, such is the competition from other European countries and with China.
He is quoted as saying that if Britain was not in the EU, Siemens would make it quite difficult for him to continue to invest in UK factories.
Siemens spokesman Rachel Odams told the Echo: "Our managing director of Siemens Industry Sector, Juergen Maier, during a round-table debate for the Sunday Times, spoke about the importance of Britain remaining in the EU.
"Juergen's key point was that leaving the EU would make inward investment from global companies, like ourselves, harder to negotiate.
"However, the UK is and will remain an important global market for Siemens.
"We have been operating here in the UK for 170 years and will continue to do so.
"In the UK we have 13 factories, including our gas turbine manufacturing facility in the centre of Lincoln as well as our state-of-the art service facility at Teal Park."
Bill Newton Dunn, Liberal Democrat MEP for the East Midlands, said: "The message from business is loud and clear. Thousands of jobs in the East Midlands every year are created by foreign investors, for whom a crucial factor is the ability to export freely to the world's largest single market.
"If we followed the lead of UKIP and many of the Tories, we would be losing that status and would be out of Europe all together, putting crucial jobs and investment at risk.
"We can better build a stronger economy by working with our European neighbours, trying to shape the rules that come out of Europe, rather than shouting from outside."
UKIP advocates leaving the EU but keeping trading links with Europe.
Prime Minister David Cameron has said a Conservative government would negotiate a new settlement with Brussels followed by an in-or-out referendum.