In a letter to 15,000 U.K. employees, signed by six senior Airbus Group (EADSY) executives, the company said that an exit from the EU could have negative consequences.

The executives who signed the letter—including Airbus COO Tom Williams and Airbus Group UK President Paul Kahn—said that if the British electorate had a “different view” in the referendum, they wouldn’t cease their U.K. operations, but a Brexit could threaten future Airbus investments in the country

“Our business model is entirely based on our ability to move products, people and ideas around Europe without any restriction and we do not believe leaving will increase the competitiveness of our British-based operations,” their letter said. “We all need to keep in the back of our minds that future investments depend very much on the economic environment in which the company operates.”

This makes Airbus only the second big U.K. employer to warn its employees about the downside of Brexit, after Rolls-Royce Motor Cars, according to the Financial Times.

Airbus UK makes the wings for almost all of its airplanes at a factory in the town of Broughton in northern Wales, the FT reports. According to the Guardian, Airbus estimates that about 100,000 jobs depend on Airbus UK’s wing operation supply chain.

It comes as little surprise that Brexit proponents were not pleased with the Airbus letter.

“Airbus shouldn’t try to frighten its employees with empty threats,” said a Vote Leave spokesperson, the FT reported. “Airbus told us we should join the euro and now they are saying we should stay in the EU at all costs. They were wrong then and they are wrong now.”