To the nine Chinese students of Arizona State University (ASU) the start of this new semester was an unexpected one.

Instead of greetings, they got detentions and denials of entry when they arrived at Los Angeles International Airport in late August. After that, a notice informing them they had to pay for their own airline ticket back to China, together with a warning of a five-year ban for re-entering the U.S. if they did not do so.

ASU said in a statement on Tuesday that no information has been given by customs. This comes after Michael Crow, the school's President sent a letter to the Secretary of State and acting Secretary of Homeland Security, demanding a written explanation.

"So far, we have not received a formal response from the federal government," said ASU in the statement.

ASU is not the only institute finding itself in a difficult place in the escalated tension between the world's two biggest economics.

"Yale has been seeking to get clarity from the federal government, about the current state of affairs," said Edward Wittenstein, director of the International Relations and Leadership Program of Yale's office of International Affairs, in an interview with CGTN Zoom In, in response to a NPR report, which says at least five graduates from China's Yenching Academy had been questioned by the FBI on espionage fears, while one graduate is a current Yale law school student.

Another report by Politico says President Donald Trump suggested at a dinner with CEOs, earlier last month, that most students from China in the U.S. could be spies.

The remark, though yet to be verified, is alarming, as it raised concerns on whether or not Washington would take stricter scrutiny over academic exchanges between the two nations, and impose further tighter rules on students' visa applications.

Citing the risk of espionage and theft of intellectual property, the U.S. has shortened the duration of visas for Chinese graduate students in aviation, robotics, and advanced manufacturing from five years to one year.

"There are legitimate national security concerns that both the United States and China may have about particular individuals or particular industries or academic subjects that are sensitive or have dual use applications," said Wittenstein, "but these have to be dealt with in a transparent and thoughtful way."

The intensified scrutiny creates a blow to U.S. universities, which have relied heavily on international students for revenue, especially after the Financial Crisis in 2008.

According to the education trade group NAFSA, foreign students contribute 39 billion U.S. dollars for America's education sector annually, which is now the country's fifth-largest service export. And one-third of the foreign students are from China, which has seen a growth from 100,000 to 360,000 enrollments (for the 2017-18 academic years) in 10 years.

However, after years of growth now a drop can be witnessed. A report by NAFSA in May shows new international student enrollment in the U.S. is down 6.6 percent in the current academic year, the first decline in a decade. On the contrary, the number of Chinese students going to the UK, Australia, and Canada has seen a rise.

Revenue problems for the universities are not the only risk. Many experts worry that education and immigration policies adopted by the Trump administration could undermine America's economic potential and its international influence in the long-term.

"By attracting the best and brightest from the around the world, the U.S. has been getting an economic free ride in terms of talent," wrote by Ryan Craig, author of College Disrupted, adding that about half of the U.S. private companies valued at one billion or more had founders who came to the U.S. as international students, including Mario Schlosser, Adam Neumann, Michelle Zatlyn, and Elon Musk.

However, given the current environment, "the next Elon Musk is much less likely to make the same decision to attend a U.S. college or university," Craig wrote.

Edward Wittenstein also echoed this view, "I'm hopeful that the escalated international relations won't spill over into higher education, because that's the investment for future."

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