Car industry leaders have backed the Remain campaign in the week of the EU referendum.
A statement from the Society of Motor Manufacturers and Traders said a vote to Leave would risk jobs.
The group's chief executive Mike Hawes told the BBC that leaving the EU would "jeopardise" the industry's continued success.
"Remaining will allow the UK to retain the influence on which the unique and successful UK automotive sector depends," Hawes said.
The BBC reported that directors at Toyota UK, Vauxhall, Jaguar Land Rover and BMW, as well as those from component makers GKN and Magal Engineering, also backed the Remain campaign.
This follows a message from the chief executive of Rolls-Royce last week in which he urged his UK employees to also vote Remain.
Roy Harvey, chairman of Vauxhall, said leaving the EU would be "undesirable" because the industry benefits from the free movement of goods and people.
Vote Leave have countered this by saying that British cars are increasingly being exported outside the EU and Brexit could provide a "boost" to the industry.
A report by the Economist Intelligence Unit earlier in June said UK car sales will decline "over the next few years" if there is a vote to leave the EU.
Prime Minister David Cameron said in a message on Twitter: "The UK car industry is clear - we should remain in the EU for a strong economy."
Former British Chambers of Commerce director general John Longworth, an advocate for Leave, told BBC Radio 4's Today programme: "The auto industry is different from the rest of industry in the sense that it has a 10 per cent tariff for cars from outside the EU.
"The biggest power in the EU - Germany - exports way more cars to the UK than we do to them, so they are not going to allow the erection of tariffs because they would damage their own industry and shoot themselves in the foot.
"Even if in a moment of madness they did, what's the worst that can happen? German cars would become a little bit more expensive, we would buy a few less and would end up buying more British-produced cars."