Stopped at the border, interrogated on national security grounds, laptops and mobile phones checked, held for several hours, plans for future research shattered. Many western scholars are nervous about travelling to China in the current political climate. But lately it is Chinese researchers working at US universities who are increasingly reporting interrogations – and in several cases deportations – at US airports, despite holding valid work or study visas for scientific research. Earlier this month the Chinese embassy in Washington said more than 70 students “with legal and valid materials” had been deported from the US since July 2021, with more than 10 cases since November 2023. The embassy said it had complained to the US authorities about each case. The exact number of incidents is difficult to verify, as the US Customs and Border Protection (CBP) agency does not provide detailed statistics about refusals at airports. A spokesperson said that “all international travellers attempting to enter the United States, including all US citizens, are subject to examination”. But testimonies have circulated on Chinese social media, and academics are becoming increasingly outspoken about what they say is the unfair treatment of their colleagues and students. “The impact is huge,” says Qin Yan, a professor of pathology at Yale School of Medicine in Connecticut, who says that he is aware of more than a dozen Chinese students from Yale and other universities who have been rejected by the US in recent months, despite holding valid visas. Experiments have stalled, and there is a “chilling effect” for the next generation of Chinese scientists. The number of people affected is a tiny fraction of the total number of Chinese students in the US. The State Department issued nearly 300,000 visas to Chinese students in the year to September 2023. But the personal accounts speak to a broader concern that people-to-people exchanges between the world’s two biggest economies and scientific leaders are straining. The refusals appear to be linked to a 2020 US rule that barred Chinese postgraduate students with links to China’s “military-civil fusion strategy”, which aims to leverage civilian infrastructure to support military development. The Australian Strategic Policy Institute thinktank estimates that 95 civilian universities in China have links to the defence sector. Nearly 2,000 visas applications were rejected on that basis in 2021. But now people who pass the security checks necessary to be granted a visa by the State Department are being turned away at the border by CBP, a different branch of government. “It is very hard for a CBP officer to really evaluate the risk of espionage,” said Dan Berger, an immigration lawyer in Massachusetts, who represents a graduate student at Yale who, midway through her PhD, was sent back from Washington’s Dulles airport in December, and banned from re-entering the US for five years. “It is sudden,” Berger said. “She has an apartment in the US. Thankfully, she doesn’t have a cat. But there are experiments that were in progress.” Academics say that scrutiny has widened to different fields – particularly medical sciences – with the reasons for the refusals not made clear. X Edward Guo, a professor of biomedical engineering at Columbia University, said that part of the problem is that, unlike in the US, military research does sometimes take place on university campuses. “It’s not black and white … there are medical universities that also do military. But 99% of those professors are doing biomedical research and have nothing to do with the military.” But “if you want to come to the US to study AI, forget it,” Guo said. One scientist who studies the use of artificial intelligence to model the impact of vaccines said he was rejected at Boston Logan International airport. He was arriving to take up a place at Harvard Medical School as a postdoctoral researcher. “I never thought I would be humiliated like this,” he wrote on the Xiaohongshu app, where he recounted being quizzed about his masters’ studies in China and asked if he could guarantee that his teachers in China had not passed on any of his research to the military. He did not respond to an interview request from the Observer. Harvard Medical School declined to confirm or comment on the specifics of individual cases, but said that “decisions regarding entry into the United States are under the purview of the federal government and outside of the school’s and the university’s jurisdiction.” The increased scrutiny comes as Beijing and Washington are struggling to come to an agreement about the US-China Science and Technology Agreement, a landmark treaty signed in 1979 that governs scientific cooperation between the two countries. Normally renewed every five years, since August it has been sputtering through six-month extensions. But following years of scrutiny from the Department of Justice investigation into funding links to China, and a rise in anti-Asian sentiment during the pandemic, ethnically Chinese scientists say the atmosphere is becoming increasingly hostile. “Before 2016, I felt like I’m just an American,” said Guo, who became a naturalised US citizen in the late 1990s. “This is really the first time I’ve thought, OK, you’re an American but you’re not exactly an American.”