LONDON: The economic argument over the cost of Britain leaving the EU heated up Thursday, with the CEO of Rolls-Royce Motor Cars telling staff that the bloc’s open borders are good for business.

Torsten Muller-Otvos said the EU’s free trade arrangements help the firm, which is owned by Germany’s BMW Group. In a letter to staff at Rolls-Royce and Mini — which is also BMW-owned — he said “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.”

Britain will hold a referendum on EU membership June 23, and economic arguments are likely to be crucial to deciding how many people vote.

Foreign-owned firms are wary of accusations of meddling in Britain’s decision. BMW head of sales and marketing Ian Robertson denied BMW was saying car prices or labor costs would definitely go up if UK leaves the EU.

He said the company was pointing out the advantages of the EU’s open market covering 28 nations and some 500 million people.

“We’ve built our business on a 500-million market called the EU, and I think that is a very successful business that we wish to continue to move forward,” Robertson told the BBC.

Britain’s Society of Motor Manufacturers and Traders said support for continued EU membership is widespread across the auto industry.