Jaguar Land Rover and Diageo Plc said a withdrawal by the U.K. from the European Union could mean new trade deals will have to be negotiated both within the region and beyond, resulting in uncertainty. Leaving the EU would be “highly damaging” and make the U.K.’s biggest carmaker’s products less competitive in Europe, JLR Chief Executive Officer Ralf Speth said in a letter to employees on Monday, provided to Bloomberg News. Remaining in the EU means Diageo benefits from trade agreements the bloc negotiates with other countries, CEO Ivan Menezes wrote in a letter to employees. The luxury unit of Tata Motors Ltd. and the world’s biggest distiller join Toyota Motor Corp. and other companies with operations in the U.K. in underlining the risks they face before a vote on Thursday over whether the country should remain in the EU. While the International Monetary Fund has warned the U.K. could slide into a recession if it leaves, manufacturers are concerned such a move would hurt exports and erode their competitiveness. Employer’s View “It would become more difficult to buy components and sell our products in our largest market,” Speth wrote employees, warning of “increasing and higher tariffs” in Europe. “This is not just an employer’s view or that of ‘big business.’ It is also the conviction of the unions who represent you.” A poll taken since the killing of pro-European lawmaker Jo Cox on Thursday and published over the weekend showed 45 percent of voters backed the ‘Remain’ camp, while 42 percent were in favor of a so-called Brexit—a turnaround from early last week when a slew of surveys put the latter group ahead. Remaining in the EU gives Diageo access to the single market, and the company benefits from free trade agreements negotiated with other countries, Menezes said. “The EU has so far concluded, or is negotiating, over 50 of these global agreements, many of which provide significant commercial benefits for Diageo,” Menezes said. “Renegotiating the U.K.’s access to our European countries and beyond would be a huge and uncertain undertaking.”