A survey released Tuesday by the U.K. auto industry lobby, the Society of Motor Manufacturers and Traders, showed 77% of its members against leaving the EU, versus 9% in favor of the so-called Brexit. The remaining 14% were undecided.

The SMMT is backed by some of the biggest investors in the U.K. overall, from Ford Motor (F) and General Motors (GM) to Toyota (TOYOF) and BMW (BYMOF). Their top concern is that their factories in the U.K. wouldn’t have equal access to the world’s largest single market if the country left the bloc.

The car industry is one of the biggest employers in the U.K., supporting 800,000 jobs directly and indirectly, with 160,000 employed in manufacturing by the big car and component makers alone. The industry had a banner year last year, with output rising to a 10-year high of 1.59 million vehicles, of which over three-quarters were exported. Over 57% of exports went to other EU markets, and even those that were sold at home or exported elsewhere depended on a supply chain that is deeply interconnected with the rest of the EU.

Tony Walker, Toyota’s deputy managing director for the U.K., told a briefing hosted by the SMMT that leaving the EU would definitely increase its costs, citing the risks of new tariffs, non-tariff barriers, customs issues, and possibly diverging regulatory standards over the long term.

Another issue for the industry is that leaving the EU—especially as the result of a vote driven largely by anti-immigrant sentiment—is that it may be harder to attract skilled workers. The free movement of labor is one of the EU’s central principles, and the industry fears that the U.K.’s chronic skills shortage would only get worse if it ripped up the current agreement on mutual recognition of things like residence rights and social security contributions.

Asked by Fortune whether they could think of a single upside to leaving, the panel of assembled industry leaders could only shrug and smile. There was no sympathy for the argument—often advanced by advocates of ‘Brexit’—that leaving would help competitiveness by lightening the regulatory burden on business.

“Do you really think that the rest of the EU is going to give the U.K. better access to its single market than it does to the other 27 members?” said Gamil Magil, chief executive of components supplier Magal Engineering.

The panel, which included representatives of BMW AG (BYMOF) and components maker GKN Plc (GKNLY), had to tread a fine line, warning about the risk to jobs from ‘Brexit’ while trying to avoid allegations of scare-mongering, which both camps in the debate accuse each other of.

“It’s not that there’s going to be a cliff effect,” of jobs immediately being cut after a vote to leave, GKN chief executive Nigel Stein told Fortune later. But, he said, it will be a lot harder for the U.K. to attract big investment decisions if it’s outside the single market. Global carmakers will be more tempted to locate new plants and projects in countries with better access, leaving the U.K. industry to wither on the vine.