A referendum on whether the UK should stay in the EU will be held on 23 June.
BMW's email said the movement of people between the UK and Europe "allows the rapid transfer of expert knowledge throughout the Rolls-Royce Motor Cars and BMW Group networks, building the skill level of our UK workforce".
It said: “The BMW Group believes that the UK is better as a member of the EU than it would be outside it.
"Free trade is important for international business. Rolls-Royce Motor Cars exports motor cars throughout the EU and imports a significant number of parts through the region.
"For BMW Group, more than half of Minis built and virtually all the engines and components made in the UK are exported to the EU, with over 150,000 new cars and many hundreds of thousands of parts imported from Europe each year.
"Tariff barriers would mean higher costs and higher prices and we cannot assume that the UK would be granted free trade with Europe from outside the EU.”
Meanwhile, more than three-quarters of members of The Society of Motor Manufacturers and Traders (SMMT), said remaining in Europe is best for their business, according to the results of a new independent survey.
The sector supports 800,000 jobs across the UK and contributes £15.5 billion to the UK economy.
The survey found that 77 percent of SMMT members said that if a referendum were held tomorrow, a ‘remain’ outcome would be best for their business, according to ComRes, who were commissioned to carry out the independent poll.
SMMT commissioned the poll over a five-week period in January and February.