Chief executives of more than 160 biotechnology companies have written an open letter to scientific journal Nature Biotechnology, expressing their “deep concern and opposition” to US President Donald Trump’s immigration ban.

The biotech leaders said America’s status as the world’s “greatest developer of medicines” was based on its ability to source researchers, clinicians and executives from around the world. Citing research published in Nature, they said 52% of the 69,000 biomedical researchers working in the US in 2014 were born overseas.

“At a stroke, the new administration has compromised years of investment in this national treasure,” the executives wrote, adding that colleagues working in the US on visas or in global outposts are now “fearful and uncertain of their status” in the wake of the ban, with some afraid to come to the US or cancelling trips.

Even though Trump’s ban has been temporarily suspended by the courts pending a legal challenge, the letter said some foreign scientists have interpreted the new administration’s message as “America is no longer welcoming of any immigrants whatsoever.”

Teva’s former CEO Jeremy Levin is reported to have organized the letter, which was signed by other well-known biotech industry leaders such as Ron Cohen, CEO of Acorda Therapeutics and chair of industry trade association BIO.

The signatories concluded: “If this misguided policy is not reversed, America is at risk of losing its leadership position in one of its most important sectors, one that will shape the world in the twenty-first century. Indeed, it will harm an industry dominated by smaller companies and startups, the very kind of industry the administration has said it wants to support. It will slow the fight against the many diseases that afflict us, as well as carry negative economic consequences for the United States.”

Unlike the biotech sector, the pharma industry has largely remained silent on the immigration issue. Trump recently heavily criticized drugmakers over their high pricing but at a meeting on Jan. 31 with pharma leaders, he promised to lower healthcare costs by “cutting regulation at a level nobody’s ever seen before.”