Rolls-Royce has written to employees to say it believes it will be better if Britain stays in the EU.
Chief executive Warren East said it would “better for employees, customers and suppliers” if there was a Remain vote.
He told BBC Radio 4’s Today programme that the uncertainty of Brexit would be bad for business.
“Our US competitors don’t have to cope with that uncertainty,” he said.
The engineering firm is increasing its manufacturing capacity but Mr East said decisions about where to invest were being put on hold.
He said not knowing whether government and EU funding would still be available in the future might affect any decision to invest in the UK over other countries.
He said: “The uncertainty and the putting decisions on hold is the problem. It’s something our competitors don’t have.”