More than three in four (77%) companies involved in the UK motor industry believe a vote to remain in Europe would be best for their business, according to a survey.
TheSociety of Motor Manufacturers and Traders (SMMT) found that 88% of members which are large companies and 73% of small and medium-sized businesses want to stay in the EU.
Some 66% of SMMT members think access to EU automotive markets has a positive impact on their firm.
The ability to hire a skilled workforce (55%) and influence industry regulations (52%) were also given as benefits of the UK's EU membership.
SMMT chief executive Mike Hawes said: "The message from UK automotive is clear - being in Europe is vital for the future of this industry and to secure jobs, investment and growth.
"UK automotive is thriving, with record car exports, new registrations and the highest manufacturing levels for a decade. Our industry supports 800,000 jobs across the UK and contributes more than £15 billion to the UK economy - our members have clearly stated that pulling out of Europe could jeopardise this."